Move toward txpostgres compatibility
Add common.BlockingRunner
Update README
Add PostgresCursorWrapper
Add NextAvailablePool
ConnectionPool runs stuff
Add untested porcelain
Clean flakes and add postgres porcelain test
Fix postgres porcelain test and add sqlite one
Remove superfluous commit
Add patches
Merge remote-tracking branch 'origin/master' into patches
Merge remote-tracking branch 'origin/pool' into patches
Patches are compatible with new, simpler runners