Change default of log_directory to 'log'

The previous default 'pg_log' might have indicated by its "pg_" prefix
that it is an internal system directory.  The new default is more in
line with the typical naming of directories with user-facing log files.
Together with the renaming of pg_clog and pg_xlog, this should clear up
that difference.

Author: Andreas Karlsson <andreas@proxel.se>

doc/src/sgml/config.sgml

@@ -4363,8 +4363,8 @@ SELECT * FROM parent WHERE key = 2400;
         find the logs currently in use by the instance. Here is an example of
         this file's content:
 <programlisting>
-stderr pg_log/postgresql.log
-csvlog pg_log/postgresql.csv
+stderr log/postgresql.log
+csvlog log/postgresql.csv
 </programlisting>
 
         <filename>current_logfiles</filename> is recreated when a new log file
@@ -4466,7 +4466,7 @@ local0.*    /var/log/postgresql
         cluster data directory.
         This parameter can only be set in the <filename>postgresql.conf</>
         file or on the server command line.
-        The default is <literal>pg_log</literal>.
+        The default is <literal>log</literal>.
        </para>
       </listitem>
      </varlistentry>

doc/src/sgml/file-fdw.sgml

@@ -262,7 +262,7 @@ CREATE FOREIGN TABLE pglog (
   location text,
   application_name text
 ) SERVER pglog
-OPTIONS ( filename '/home/josh/9.1/data/pg_log/pglog.csv', format 'csv' );
+OPTIONS ( filename '/home/josh/data/log/pglog.csv', format 'csv' );
 </programlisting>
   </para>
 

src/backend/utils/misc/guc.c

@@ -3320,7 +3320,7 @@ static struct config_string ConfigureNamesString[] =
 			GUC_SUPERUSER_ONLY
 		},
 		&Log_directory,
-		"pg_log",
+		"log",
 		check_canonical_path, NULL, NULL
 	},
 	{

src/backend/utils/misc/postgresql.conf.sample

@@ -344,7 +344,7 @@
 					# (change requires restart)
 
 # These are only used if logging_collector is on:
-#log_directory = 'pg_log'		# directory where log files are written,
+#log_directory = 'log'			# directory where log files are written,
 					# can be absolute or relative to PGDATA
 #log_filename = 'postgresql-%Y-%m-%d_%H%M%S.log'	# log file name pattern,
 					# can include strftime() escapes

src/test/perl/PostgresNode.pm

@@ -551,7 +551,7 @@ sub _backup_fs
 		$backup_path,
 		filterfn => sub {
 			my $src = shift;
-			return ($src ne 'pg_log' and $src ne 'postmaster.pid');
+			return ($src ne 'log' and $src ne 'postmaster.pid');
 		});
 
 	if ($hot)

src/test/perl/RecursiveCopy.pm

@@ -48,9 +48,9 @@ attempted.
 
  RecursiveCopy::copypath('/some/path', '/empty/dir',
     filterfn => sub {
-		# omit pg_log and contents
+		# omit log/ and contents
 		my $src = shift;
-		return $src ne 'pg_log';
+		return $src ne 'log';
 	}
  );