Implement RegexIterator::INVERT_MATCH

Summary: Closes https://github.com/facebook/hhvm/pull/3718

Reviewed By: @sgolemon

Differential Revision: D1547317
Re-fix CMake jemalloc check

Summary: Get rid of backslashes that nobody
fully understands and add 0x to the version
constant, 'cause it's supposed to be hex.

Reviewed By: @fredemmott

Differential Revision: D1547859