automatically attempt to convert all hack test inputs

Summary: check files
Fixes https://github.com/facebook/hhvm/issues/4218

Reviewed By: @jwatzman

Differential Revision: D1682211

Signature: t1:1682211:1415999283:9b1db0f1d25a170335453f1917500d00332a500c
support for enums

Summary: This converts first class enums. We convert it into a final class with a private constructor
and use a trait to implement all the enum methods.
Fixes https://github.com/facebook/hhvm/issues/4221

Reviewed By: @jwatzman

Differential Revision: D1682688

Signature: t1:1682688:1416003415:c4522a703537d9b3c1603808a08e8a98749d6660