Database doesn't unlock when DVCS Error raised

[ksurya]

If for some strange reasons, scipy_central.filestorage.dvsc_wrapper.DVCRepo.run_dvcs_command() don't properly execute either by raising exception or does not respond while submitting an entry, submissions are still stored in database! For this we need to have TransactionMiddleware.

But upon adding Transaction Middleware, if DVCS Error is raised, database doesn't get unlocked. The server has to be restarted again..

Update: PostgreSQL seems to handle this database lock! Probably, concurrency problem with Sqlite.
However we need to optimize this feature

[ksurya]

This bug does not happen to come back after #168