Renumber GUC_* constants.
Renumber GUC_* constants.

This moves all the regular flags back together (for aesthetic reasons), and
makes room for more GUC_UNIT_* types.

50wu/gpdb,pavanvd/postgres-xl,ashwinstar/gpdb,adam8157/gpdb,50wu/gpdb,50wu/gpdb,jmcatamney/gpdb,pavanvd/postgres-xl,jmcatamney/gpdb,xinzweb/gpdb,pavanvd/postgres-xl,oberstet/postgres-xl,xinzweb/gpdb,Postgres-XL/Postgres-XL,50wu/gpdb,techdragon/Postgres-XL,adam8157/gpdb,ovr/postgres-xl,zeroae/postgres-xl,xinzweb/gpdb,adam8157/gpdb,lisakowen/gpdb,lisakowen/gpdb,greenplum-db/gpdb,oberstet/postgres-xl,50wu/gpdb,adam8157/gpdb,adam8157/gpdb,lisakowen/gpdb,oberstet/postgres-xl,yazun/postgres-xl,zeroae/postgres-xl,ashwinstar/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,adam8157/gpdb,lisakowen/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,Postgres-XL/Postgres-XL,adam8157/gpdb,techdragon/Postgres-XL,oberstet/postgres-xl,ashwinstar/gpdb,ovr/postgres-xl,zeroae/postgres-xl,ashwinstar/gpdb,ovr/postgres-xl,greenplum-db/gpdb,Postgres-XL/Postgres-XL,yazun/postgres-xl,oberstet/postgres-xl,xinzweb/gpdb,Postgres-XL/Postgres-XL,adam8157/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,pavanvd/postgres-xl,zeroae/postgres-xl,greenplum-db/gpdb,xinzweb/gpdb,zeroae/postgres-xl,ashwinstar/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,xinzweb/gpdb,Postgres-XL/Postgres-XL,50wu/gpdb,yazun/postgres-xl,xinzweb/gpdb,xinzweb/gpdb,techdragon/Postgres-XL,50wu/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,lisakowen/gpdb,50wu/gpdb,jmcatamney/gpdb,yazun/postgres-xl,lisakowen/gpdb,techdragon/Postgres-XL,ashwinstar/gpdb,ovr/postgres-xl,techdragon/Postgres-XL,lisakowen/gpdb,greenplum-db/gpdb,pavanvd/postgres-xl,ovr/postgres-xl,jmcatamney/gpdb,yazun/postgres-xl,lisakowen/gpdb