Rework `run_pending_requests` to avoid re-ordering requests
Rework `run_pending_requests` to avoid re-ordering requests

We now iterate through all the items in `_pending_reqs`, and exit when
we're done iterating it, or if `can_run_requests` returns false.

devnexen/h2o,devnexen/h2o,cwyang/h2o,lkwg82/h2o,rayrapetyan/h2o,devnexen/h2o,deweerdt/h2o,h2o/h2o,h2o/h2o,yannick/h2o,zlm2012/h2o,cwyang/h2o,cwyang/h2o,deweerdt/h2o,cwyang/h2o,cwyang/h2o,devnexen/h2o,yannick/h2o,lkwg82/h2o,yannick/h2o,rayrapetyan/h2o,lkwg82/h2o,h2o/h2o,deweerdt/h2o,yannick/h2o,devnexen/h2o,yannick/h2o,lkwg82/h2o,devnexen/h2o,yannick/h2o,cwyang/h2o,lkwg82/h2o,yannick/h2o,lkwg82/h2o,deweerdt/h2o,rayrapetyan/h2o,cwyang/h2o,h2o/h2o,devnexen/h2o,h2o/h2o,zlm2012/h2o,lkwg82/h2o,lkwg82/h2o,zlm2012/h2o,deweerdt/h2o,zlm2012/h2o,deweerdt/h2o,cwyang/h2o,devnexen/h2o,deweerdt/h2o,rayrapetyan/h2o,rayrapetyan/h2o,rayrapetyan/h2o,zlm2012/h2o,deweerdt/h2o,devnexen/h2o,rayrapetyan/h2o,h2o/h2o,zlm2012/h2o,rayrapetyan/h2o,rayrapetyan/h2o,zlm2012/h2o,h2o/h2o,h2o/h2o,yannick/h2o,h2o/h2o,rayrapetyan/h2o,deweerdt/h2o,lkwg82/h2o,zlm2012/h2o,yannick/h2o,zlm2012/h2o