Recognize infinite loops as terminal.

Reviewed By: @elgenie

Differential Revision: D1568254
Fix terminality handling of do loops with 'continue'

Reviewed By: @elgenie

Differential Revision: D1568260
Assume valid srcs in cgLdPackedArrayElem() and cgCheckPackedArrayElemNull()

Summary: These were complex enough to split out into their own diff.

Reviewed By: @alexmalyshev

Differential Revision: D1566071
Allow profiling/jitting of warmup requests

Summary: With JitProfileWarmupRequests=true, and NumSingleJitRequests=0 we
should be back to the old way of doing things.

Reviewed By: @edwinsmith

Differential Revision: D1568113