swift234

Now that we have contextual type information more generally available, start
using it to improve closure diagnostics by inferring the types of otherwise
untyped closure paramdecls from this context information.  This 
resolves:

<rdar://problem/20371273> Type errors inside anonymous functions don't provide enough information
producing 
  error: binary operator '==' cannot be applied to operands of type 'Int' and 'UInt'
  note: overloads for '==' exist with these partially matching parameter lists: (UInt, UInt), (Int, Int)

and:
<rdar://problem/20978044> QoI: Poor diagnostic when using an incorrect tuple element in a closure
producing:
error: value of tuple type '(Int, Int)' has no member '2'

and probably a lot more.  We're still limited from getting things like "foo.map {...}" because 
we're not doing type subsitutions from the base into the protocol extension member.



Swift SVN r30971