fix backtrace printed when cannot get lock.
change lock error handling code so exceptions have useful info and
exception handling in one place.
add test case for when cannot get lock.
pulling from ../source
abort: pretxncommit hook exited with status 1
transaction abort!
rollback completed
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added 1 changesets with 1 changes to 1 files
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1 files, 2 changesets, 2 total revisions