R1:85011a46d0aa

Bail out of PhabricatorRepositoryGraphCache more aggressively after cache fills

Summary:
Ref PHI109. Ref T11786. We currently test elapsed time every 64 iterations (since iterations are normally very fast), but at least one install is seeing the page timeout after 30 seconds.

One reason could be that cache fills may occur, and are likely to be much slower than normal iterations. In an extreme case, we could do 64 cache fills before checking the time. Tweak thing so that we always check the time after…