Fix usage string for oid2name

Seems the usage message for oid2name calls it pg_oid2name.  Fixed.

--
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073
Index: contrib/oid2name/oid2name.c
===================================================================
RCS file: /cvsroot/pgsql-server/contrib/oid2name/oid2name.c,v
retrieving revision 1.22
diff -c -c -r1.22 oid2name.c
*** contrib/oid2name/oid2name.c    4 Aug 2003 00:43:11 -0000    1.22
--- contrib/oid2name/oid2name.c    3 Mar 2004 14:23:18 -0000
***************
*** 158,164 ****
              case '?':
              case 'h':
                  fprintf(stderr, "\
! Usage: pg_oid2name [-d database [-x] ] [-t table | -o oid]\n\
          default action        display all databases\n\
          -d database           database to oid2name\n\
          -x                    display system tables\n\
--- 158,164 ----
              case '?':
              case 'h':
                  fprintf(stderr, "\
! Usage: oid2name [-d database [-x] ] [-t table | -o oid]\n\
          default action        display all databases\n\
          -d database           database to oid2name\n\
          -x                    display system tables\n\