failing test for #2495
fix #2498
replace `store_error()` with `store_result()`
remove commented code
Merge pull request #2531 from gittip/fix-2498

Fix 2498
Bump version to 13.2.5
Bump version to 13.2.5-dev
remove obsolete comment
update stats in a single request at the end of payday
remove gittip/billing/steady_state.py