This cleans up the code a lot, and takes it out of various hot
paths. It will impact perf for requests where intercepts are used,
but no longer penalizes requests that don't use intercepts.
This reduces CPU instruction count by about 0.2%, has negligible impact on other metrics. Implementation has been changed a but upon discussion with @mwilliams to account for circular destruction. The question remains open whether this should be in before or after rooting out hphpc, but on the other hand we gotta do what we gotta do to move forward.
This change is mostly for FB internal organizational reasons.
Building is not effected beyond the fact that the target now
lands in hphp/hhvm/hhvm rather than src/hhvm/hhvm.
Mark Williams