Remove obsolete example of CSV log file name from log_filename document.

7380b63 changed log_filename so that epoch was not appended to it
when no format specifier is given. But the example of CSV log file name
with epoch still left in log_filename document. This commit removes
such obsolete example.

This commit also documents the defaults of log_directory and
log_filename.

Backpatch to all supported versions.

Christoph Berg

Author: MasaoFujii

doc/src/sgml/config.sgml

@@ -3057,6 +3057,7 @@ 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>.
        </para>
       </listitem>
      </varlistentry>
@@ -3082,6 +3083,7 @@ local0.*    /var/log/postgresql
         </ulink> specification.
         Note that the system's <systemitem>strftime</systemitem> is not used
         directly, so platform-specific (nonstandard) extensions do not work.
+        The default is <literal>postgresql-%Y-%m-%d_%H%M%S.log</literal>.
        </para>
        <para>
         If you specify a file name without escapes, you should plan to
@@ -3098,8 +3100,6 @@ local0.*    /var/log/postgresql
         log file name to create the file name for CSV-format output.
         (If <varname>log_filename</> ends in <literal>.log</>, the suffix is
         replaced instead.)
-        In the case of the example above, the CSV
-        file name will be <literal>server_log.1093827753.csv</literal>.
        </para>
        <para>
         This parameter can only be set in the <filename>postgresql.conf</>