Commit of a *MAJOR* patch from Dan McGuirk <djm@indirect.com>

Changes:

        * Unique index capability works using the syntax 'create unique
          index'.

        * Duplicate OID's in the system tables are removed.  I put
          little scripts called 'duplicate_oids' and 'find_oid' in
          include/catalog that help to find and remove duplicate OID's.
          I also moved 'unused_oids' from backend/catalog to
          include/catalog, since it has to be in the same directory
          as the include files in order to work.

        * The backend tries converting the name of a function or aggregate
          to all lowercase if the original name given doesn't work (mostly
          for compatibility with ODBC).

        * You can 'SELECT NULL' to your heart's content.

        * I put my _bt_updateitem fix in instead, which uses
          _bt_insertonpg so that even if the new key is so big that
          the page has to be split, everything still works.

        * All literal references to system catalog OID's have been
          replaced with references to define'd constants from the catalog
          header files.

        * I added a couple of node copy functions.  I think this was a
          preliminary attempt to get rules to work.

src/include/access/gist.h

@@ -174,7 +174,7 @@ extern void gistbuild(Relation heap,
 	  FuncIndexInfo *finfo,
 	  PredInfo *predInfo);
 extern InsertIndexResult gistinsert(Relation r, Datum *datum,
-			char *nulls,ItemPointer ht_ctid);
+			char *nulls,ItemPointer ht_ctid, bool is_update);
 extern void _gistdump(Relation r);
 extern char *text_range_out(TXTRANGE *r);
 extern char *int_range_out(INTRANGE *r);