In the interpreter, neither ContEnter nor ContExit checked the
surprise flags, resulting in the time being attributed to the
callers. In the jit, ContEnter checked the surprise flags, but
ContExit did not, resulting in what appeared to be highly
recursive profiles.
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.