Issue 518: java.sql.Connection.commit() freezes after LOB modification with EXCLUSIVE connection    

Improve error message when dropping an index that belongs to a constraint, specify constraint in error message.

MVStore: closing a map and making it read-only is now only a marker and not enforced, to allow concurrent store operations

Fix performance regression for: Fix bug with ALLOW_LITERALS=NONE, where the periodic analyze table on insert would throw an exception.