Rollback any pending transactions prior to reloading schema

[raizyr]

Issue #26 appears to be related to aggressive locking that is not present in sqlite. Issuing a session.rollback() prior to reloading schema seems to fix the hanging.

[stevearc]

Have you tested this? I feel like you would have to call transaction.abort() instead of self.db.rollback() since the engine is using the zope transaction extension.

[raizyr]

I have tested insofar as I'm currently using a patched version. In tracking it down, the schema drop seemed to be waiting on a lock caused by SqlCache.distinct, although I couldn't find any indication of why a query would lock. Adding the self.db.rollback stopped the waiting for lock.

[stevearc]

Fair enough. I'll merge this into the 0.2 branch and cut a new release