Move coefficient test to FBOnly location

Summary: - hphp/test/ is open-source (https://github.com/facebook/hhvm/commit/cee09b7437b120c8c1cc4949613840cc89f3ba44)
 - the implementation of this class isn't (FB: D1521758)
 - this will have broken OSS builds. We pushed it anyway as we only run quick/
 - also, there shouldn't really be new top-level files in hphp/test/slow/

Reviewed By: @JoelMarcey

Differential Revision: D1527799
More cleanup on the relocator

Summary: More refactoring to support live relocation. This fixes
a few edge cases, which only show up if you relocate two adjacent
tracelets to two disjoint regions (essentially you have to be very
careful about where you remap the "in-between" address).

Also finding that some of the reformatting keeps conflicting with
other peoples diffs (especially vasm) - so wanted to get it in
sooner rather than later.

Reviewed By: @edwinsmith

Differential Revision: D1523462