More changes for temporary tables:
+ Arrange to use a nonmutable schema source for temporary table declarations.  Modify PE.g to
  ensure that we flip back to nonddl mode when handling temporary table declarations.
+ Add startup/shutdown catalog cleanup methods, which remove any user_temp_table rows for the
  local server.  Also add a membership listener that force closes all connections with temporary
  tables upon the local member leaving the quorum.
+ Restructure some of the emitter around drop tables in order to support dropping temporary tables
  on databases that have already been dropped.
+ Arrange for worker groups that are pinned to not be recycled upon statement finish.
+ Arrange for SSConnection to drop any outstanding temporary tables upon close.
Make debug log less noisy.