to give us a thread dump when they get stuck

About #385 

Fix multi-threaded mode insert exception "Unique index or primary key violation", test case by Anatolii K

so we get nicer error messages when things fail

when run in memory mode, the initial connection used a memory DB,while
the second connection used a disk DB

doing DROP ALL OBJECTS

leads to an NPE when the session closes

mostly because they rely on closing and re-opening the DB

generated by unit tests