Update cmake files to require jemalloc >= 3.5.1

Summary: @jasone landed a diff this morning which requires the allocx()
APIs in jemalloc.  Provide a useful error message if our version is
too old.

Reviewed By: @JoelMarcey

Differential Revision: D1545626
Add T_FINALLY to constants

Summary: Fixes #3703
Closes https://github.com/facebook/hhvm/pull/3708

Reviewed By: @sgolemon

Differential Revision: D1544682
make class closure consist with PHP

Summary: See #3431
Closes https://github.com/facebook/hhvm/pull/3460

Reviewed By: @sgolemon

Differential Revision: D1496023