Add most of 5.6 GMP support

Summary: GMP resources are now objects.  There are now warnings were there were none before. We are still lacking GMP object arithmatic, bitwise, and comparison overloading from 5.6.

Some tests are still failing, either due to lack of implementation (object overloading), slight differences between HHVM and PHP (Bad serialization data handling), or because the PHP test actually is bad (has bad result in test).

In PHP 5.6 GMP tests were mostly renamed to match their functionality.  We had both copies of tests (001, 002, etc, and named tests), so I deleted duplicate tests favouring the new named copies.  The command I used to find duplicates is:

find -type f -exec md5sum '{}' ';' | sort | uniq --all-repeated=separate -w 33 | cut -c 35-

Implements most of #3791

Closes https://github.com/facebook/hhvm/pull/4267

Reviewed By: @JoelMarcey

Differential Revision: D1688019

Signature: t1:1688019:1418359695:f8a534bb1582f5d2a30f0279f12e09e53647301c