Add OldSnapshotTimeMapLock to wait_event table in docs.
Add OldSnapshotTimeMapLock to wait_event table in docs.

Ashutosh Sharma with minor fixes by me.

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