Fix integer overflow in chunk_split

Reviewed By: @ptarjan

Differential Revision: D1515947
folly fix in third-party
Add mcrypt constants to hhi

Summary: As the title says.
Closes https://github.com/facebook/hhvm/pull/3594

Reviewed By: @sgolemon

Differential Revision: D1519199
Rename namespace JIT to jit

Summary: that's it. I also added some std:: qualifiers in tc-print to follow
the style we're using and break a few ambiguities.

Reviewed By: @billf

Differential Revision: D1517327