973784 - improving performance of depsolve

Using the pre-calculated serialized version and release as stored in the database to do version comparison rather than re-calculating on the fly. This along with a couple of other tweaks has resulted in a 40x speedup.

https://bugzilla.redhat.com/show_bug.cgi?id=973784
What motivated this change? an empty tuple and None both evaluate to False, so both the old and new versions seem to affect the if statement on line 304 the same.