Change return type of LdRef to InitCell

Summary: Boxes can't contain Uninit.

Reviewed By: @swtaarrs

Differential Revision: D1436506
Corrected the debug output and classname of Closure objects to match php

Summary: our output of `var_dump` and `get_class` of closure objects was different tan php's. Correcting it made several bad zend tests pass!

Reviewed By: @ptarjan

Differential Revision: D1402833
Share errors for abstract trait methods and interfaces

Summary: Abstract trait methods were not checked for same compliance as interfaces. Found via a bad zend test

Reviewed By: fredemmott, eletuchy

Differential Revision: D1395699