Changed the way to check for Closure::bind to support HHVM
Added a class patch to allow doubling exceptions on HHVM
Fixed the detection on unknown class typehints on HHVM

This fix should also allow supporting HHVM scalar typehints when they are
used, thus keeping the signature compatible.
Fixed the spec checking for private method on HHVM

HHVM does not yet define the private __clone method on ReflectionClass, so
the spec was failing. The HHVM incompatibility has been reported as
https://github.com/facebook/hhvm/issues/1572
Marked HHVM as officially supported by enforcing it on Travis
Merge pull request #72 from stof/hhvm_compatibility

HHVM compatibility