Alias manager does not know that generator parameters are populated and
assumes they are uninit. The current code works because control flow
algorithm gives up while trying to deal with the continuation switch
statement full of gotos.
This diff fixes it by setting isGeneratorParameter flag in symbols
representing parameters of enclosing generator wrapper and use variables
of enclosing closure.
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.
jan