Assert: fixed exception() return with user handler [Closes #149]
Merge pull request #150 from milo/pull-fix-149

Assert: fixed exception() return
Rename PhpExecutable to ZendPhpExecutable
Added IPhpExecutable, abstracted from ZendPhpExecutable
Added HhvmPhpExecutable, added detection for php/hhvm binary type
Enable HHVM runs on Travis