HBASE-9421 Provide better error message when dropping non-existent namespace (Ted Yu)



git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1520043 13f79535-47bb-0310-9956-ffa450edef68
HBASE-9387 Region could get lost during assignment (Ted Yu)



git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1520058 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd
Merge remote branch 'origin/trunk-gd' into fb-HBASE-8584-trunk-gd