filter_id should return null for arrays

Summary: Found via a bad zend test

Reviewed By: @JoelMarcey

Differential Revision: D1388346
Added passing tests as an xargs output file

Summary: This diff modifies the test runner to create a file of all passing tests. This is especially useful when dealing with `zend/bad`

Reviewed By: @fredemmott

Differential Revision: D1385647
don't process trait aliases in repo mode

Summary: The number calculated by ##Class::loadUsedTraits## is not
 used in repo mode. As a result, iterating over the trait alias rules
 to estimate how many functions are aliased isn't necessary, since all
 the functions in question have already been flattened into the preclass

Reviewed By: @ottoni

Differential Revision: D1387170
Remove m_hLoad field from MixedArray

Summary: If MixedArray's m_used field didn't move backwards (aside from compact),
then we would have a nice invariant where m_hLoad is always less than or
equal to m_used, making the m_hLoad field unnecessart.

This diff changes MixedArray so that m_used never moves backwards (aside
from compact), and it removes all the logic that checks or maintains the
m_hLoad field.

Reviewed By: @jdelong

Differential Revision: D1386785
Added Stash Caching Library to Framework Tests

Summary: Stash currently works on HHVM. It has some complex behavior that may be good to continue testing against.
Closes #2955

Reviewed By: @fredemmott

Differential Revision: D1386977

Pulled By: @JoelMarcey