Minor Obs_storage refactoring (move code around).
Client bugfix: stopped reading responses after getting an unexpected one.
Implement deadlock detection and recovery (by killing most recent TX(s)).
More deadlock detection tests.
Deadlock detection must not cross the keyspace boundaries.
Perform deadlock check only on lock acquisition timeout.
Perform only one deadlock check per period (per keyspace).
Limit concurrency in Test_00util.lwt_tests.
Correct deadlock detection involving shared locks.
Merge branch 'deadlock-detection'

Conflicts:
	src/ob_repl.ml
	src/server/obs_storage.ml
Implement "DEBUG txs" and "DEBUG tx id" commands in REPL.
Disambiguate DEBUG TXS output (held vs. wanted locks).
Minor tweaks in DEBUG TXS output.