rewrite the payin loop in SQL
after a crash don't rerun the stages that were successfully completed
add some log messages
run a DB check at the end of the payout loop
drop the `pending` column
update tests
improve test coverage of gittip.billing.exchanges
fix VCR replay
remove PaydayHarness class
remove a log message
trick the coverage measurement
upgrade balanced
100% test coverage for gittip.billing.payday
reduce the number of Balanced API requests
fix test
make participant IDs stable across test runs
update test fixtures