Clean up $pid1 and $pid2 global variables in tests.

(also, use Integer() instead of #to_i)
Possibly better way for knowing if we're in a transaction
Spec Que::Migrations.in_transaction? more thoroughly.
Get specs passing on Ruby 1.9.
Officially support 1.9.3.
Merge branch 'cleanup-global' of https://github.com/joevandyk/que