Fix pg_dump docs to acknowledge that you can use -Z with plain text output. Pointed out by Daniel Migowski.

doc/src/sgml/ref/pg_dump.sgml

@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/pg_dump.sgml,v 1.81.2.3 2006/05/13 17:11:02 momjian Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/pg_dump.sgml,v 1.81.2.4 2008/08/26 00:03:36 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -497,9 +497,14 @@ PostgreSQL documentation
       <term><option>--compress=<replaceable class="parameter">0..9</replaceable></option></term>
       <listitem>
        <para>
-        Specify the compression level to use in archive formats that
-        support compression.  (Currently only the custom archive
-        format supports compression.)
+        Specify the compression level to use.  Zero means no compression.
+        For the custom archive format, this specifies compression of
+        individual table-data segments, and the default is to compress
+        at a moderate level.
+        For plain text output, setting a nonzero compression level causes
+        the entire output file to be compressed, as though it had been
+        fed through <application>gzip</>; but the default is not to compress.
+        The tar archive format currently does not support compression at all.
        </para>
       </listitem>
      </varlistentry>