Disable spilling into MMX registers
Filter strict_warnings like notices

There is a runtime option to filter out notices and warnings,
but strict_warnings were left out. Bundle them with notices.

We raise a lot of strict_warnings; and when we fix hphpiCompat
(to match zend better) we will raise a lot more, so this could
matter.
Fix ref generator parameters

Alias manager does not know whether generator parameters are passed by
reference. This didn't matter, because every generator had at least one
function call (hphp_continuation_done()) that pretty much disabled unused
variable elimination.

This diff fixes that, lets us get rid of artificial function calls in
generators and will allow later improvements in alias manager.