Fix lookupCnsU

Summary: Looking up constants with fallback was broken since the return value
would never be filled in.  This was breaking composer init.

Reviewed By: @markw65

Differential Revision: D1472130
Fix error for (Recursive)CachingIterator::ctor's param 1

Summary: Fixed the TODO

Was this from when HipHopSyntax wasn't available?
Closes https://github.com/facebook/hhvm/pull/3351

Reviewed By: @elgenie

Differential Revision: D1475170

Pulled By: svcscm
typechecker: cleaner variable names in sub_type

Summary: ... when both args have the same type and order matters,
 the names matter as well; ##ty1## and ##ty2## don't communicate
 much about their presumed subtype relationship.

Reviewed By: @jwatzman

Differential Revision: D1466669
typechecker: typing new static() [2/3]

Summary: Enforce "descendants of this class must have compatible
 `__construct` declarations", due to either properties of the
 class/`__construct` method, or due to the use of the
 `<<ConsistentConstruct>>` attribute.

Reviewed By: @jwatzman

Differential Revision: D1466669