Moves behavior in api_comment that updates stateful counters and
generates notifications into a function which can also be called
if a filtered comment is approved. Fixes#272.
Incidentally, also fixes#278 by adding another filter to the post
subscribers query during general clean-up/refactoring.
Originally was going to move this function into the Comments model,
since assurances about state (even with side effects) should probably
be made there, but I couldn't find a sane way to untangle the imports.
f5f2c008ad