pg_upgrade: trim down --help and doc option descriptions

Previous code had old/new prefixes on option values, e.g.
--old-datadir=OLDDATADIR.  Remove them, for simplicity;  now:
--old-datadir=DATADIR.  Also update docs to do the same.

contrib/pg_upgrade/option.c

@@ -229,17 +229,17 @@ usage(void)
   pg_upgrade [OPTION]...\n\
 \n\
 Options:\n\
-  -b, --old-bindir=OLDBINDIR    old cluster executable directory\n\
-  -B, --new-bindir=NEWBINDIR    new cluster executable directory\n\
+  -b, --old-bindir=BINDIR      old cluster executable directory\n\
+  -B, --new-bindir=BINDIR       new cluster executable directory\n\
   -c, --check                   check clusters only, don't change any data\n\
-  -d, --old-datadir=OLDDATADIR  old cluster data directory\n\
-  -D, --new-datadir=NEWDATADIR  new cluster data directory\n\
+  -d, --old-datadir=DATADIR     old cluster data directory\n\
+  -D, --new-datadir=DATADIR     new cluster data directory\n\
   -j, --jobs                    number of simultaneous processes or threads to use\n\
   -k, --link                    link instead of copying files to new cluster\n\
   -o, --old-options=OPTIONS     old cluster options to pass to the server\n\
   -O, --new-options=OPTIONS     new cluster options to pass to the server\n\
-  -p, --old-port=OLDPORT        old cluster port number (default %d)\n\
-  -P, --new-port=NEWPORT        new cluster port number (default %d)\n\
+  -p, --old-port=PORT           old cluster port number (default %d)\n\
+  -P, --new-port=PORT           new cluster port number (default %d)\n\
   -r, --retain                  retain SQL and log files after success\n\
   -U, --username=NAME           cluster superuser (default \"%s\")\n\
   -v, --verbose                 enable verbose internal logging\n\
@@ -252,10 +252,10 @@ Before running pg_upgrade you must:\n\
   shutdown the postmaster servicing the new cluster\n\
 \n\
 When you run pg_upgrade, you must provide the following information:\n\
-  the data directory for the old cluster  (-d OLDDATADIR)\n\
-  the data directory for the new cluster  (-D NEWDATADIR)\n\
-  the \"bin\" directory for the old version (-b OLDBINDIR)\n\
-  the \"bin\" directory for the new version (-B NEWBINDIR)\n\
+  the data directory for the old cluster  (-d DATADIR)\n\
+  the data directory for the new cluster  (-D DATADIR)\n\
+  the \"bin\" directory for the old version (-b BINDIR)\n\
+  the \"bin\" directory for the new version (-B BINDIR)\n\
 \n\
 For example:\n\
   pg_upgrade -d oldCluster/data -D newCluster/data -b oldCluster/bin -B newCluster/bin\n\

doc/src/sgml/pgupgrade.sgml

@@ -79,15 +79,15 @@
     <variablelist>
 
      <varlistentry>
-      <term><option>-b</option> <replaceable>old_bindir</></term>
-      <term><option>--old-bindir=</option><replaceable>old_bindir</></term>
+      <term><option>-b</option> <replaceable>bindir</></term>
+      <term><option>--old-bindir=</option><replaceable>bindir</></term>
       <listitem><para>the old cluster executable directory;
       environment variable <envar>PGBINOLD</></para></listitem>
      </varlistentry>
 
      <varlistentry>
-      <term><option>-B</option> <replaceable>new_bindir</></term>
-      <term><option>--new-bindir=</option><replaceable>new_bindir</></term>
+      <term><option>-B</option> <replaceable>bindir</></term>
+      <term><option>--new-bindir=</option><replaceable>bindir</></term>
       <listitem><para>the new cluster executable directory;
       environment variable <envar>PGBINNEW</></para></listitem>
      </varlistentry>
@@ -99,15 +99,15 @@
      </varlistentry>
 
      <varlistentry>
-      <term><option>-d</option> <replaceable>old_datadir</></term>
-      <term><option>--old-datadir=</option><replaceable>old_datadir</></term>
+      <term><option>-d</option> <replaceable>datadir</></term>
+      <term><option>--old-datadir=</option><replaceable>datadir</></term>
       <listitem><para>the old cluster data directory; environment
       variable <envar>PGDATAOLD</></para></listitem>
      </varlistentry>
 
      <varlistentry>
-      <term><option>-D</option> <replaceable>new_datadir</></term>
-      <term><option>--new-datadir=</option><replaceable>new_datadir</></term>
+      <term><option>-D</option> <replaceable>datadir</></term>
+      <term><option>--new-datadir=</option><replaceable>datadir</></term>
       <listitem><para>the new cluster data directory; environment
       variable <envar>PGDATANEW</></para></listitem>
      </varlistentry>
@@ -140,15 +140,15 @@
      </varlistentry>
 
      <varlistentry>
-      <term><option>-p</option> <replaceable>old_port_number</></term>
-      <term><option>--old-port=</option><replaceable>old_portnum</></term>
+      <term><option>-p</option> <replaceable>port</></term>
+      <term><option>--old-port=</option><replaceable>port</></term>
       <listitem><para>the old cluster port number; environment
       variable <envar>PGPORTOLD</></para></listitem>
      </varlistentry>
 
      <varlistentry>
-      <term><option>-P</option> <replaceable>new_port_number</></term>
-      <term><option>--new-port=</option><replaceable>new_portnum</></term>
+      <term><option>-P</option> <replaceable>port</></term>
+      <term><option>--new-port=</option><replaceable>port</></term>
       <listitem><para>the new cluster port number; environment
       variable <envar>PGPORTNEW</></para></listitem>
      </varlistentry>
@@ -161,8 +161,8 @@
      </varlistentry>
 
      <varlistentry>
-      <term><option>-U</option> <replaceable>user_name</></term>
-      <term><option>--username=</option><replaceable>user_name</></term>
+      <term><option>-U</option> <replaceable>username</></term>
+      <term><option>--username=</option><replaceable>username</></term>
       <listitem><para>cluster's super user name; environment
       variable <envar>PGUSER</></para></listitem>
      </varlistentry>