Fix dependency detection issue with "attribute :foo;" statements

Summary: When an XHP class imports attributes from another XHP class via the
"attribute :foo;" syntax, we need to record the dependency to make sure
typechecking is performed in the correct order.

Reviewed By: @elgenie, @jwatzman

Differential Revision: D1740731

Signature: t1:1740731:1418685342:7d2db3991a19b1c1385cf2fcbbe61e3f90b2f425
Remove unused includes in builtin-functions.h

Summary: It was pulling in a bunch of stuff it didn't need.

Reviewed By: @edwinsmith

Differential Revision: D1735483

Signature: t1:1735483:1418393005:a26842d02f0fd19a4d44e1dabe0d6d18af1d1609