Various fixes to "ALTER ... SET/RESET" tab completions
Various fixes to "ALTER ... SET/RESET" tab completions

Add
- ALTER SYSTEM SET/RESET ... -> GUC variables
- ALTER TABLE ... SET WITH -> OIDS
- ALTER DATABASE/FUNCTION/ROLE/USER ... SET/RESET -> GUC variables
- ALTER DATABASE/FUNCTION/ROLE/USER ... SET ... -> FROM CURRENT/TO
- ALTER DATABASE/FUNCTION/ROLE/USER ... SET ... TO/= -> possible values

Author: Fujii Masao
Reviewed-by: Michael Paquier, Masahiko Sawada

greenplum-db/gpdb,adam8157/gpdb,xinzweb/gpdb,greenplum-db/gpdb,lisakowen/gpdb,adam8157/gpdb,xinzweb/gpdb,50wu/gpdb,50wu/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,adam8157/gpdb,lisakowen/gpdb,adam8157/gpdb,jmcatamney/gpdb,lisakowen/gpdb,xinzweb/gpdb,lisakowen/gpdb,adam8157/gpdb,adam8157/gpdb,ashwinstar/gpdb,50wu/gpdb,lisakowen/gpdb,50wu/gpdb,50wu/gpdb,50wu/gpdb,xinzweb/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb,jmcatamney/gpdb,50wu/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,adam8157/gpdb,lisakowen/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,lisakowen/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,xinzweb/gpdb,ashwinstar/gpdb,adam8157/gpdb,ashwinstar/gpdb,xinzweb/gpdb,xinzweb/gpdb