* Give Sequence a top-level Element, constrain Iterator to match
* Remove many instances of Iterator.
* Fixed various hard-coded tests
* XFAIL a few tests that need further investigation
* Change assoc type for arrayLiteralConvertible
* Mop up remaining "better expressed as a where clause" warnings
* Fix UnicodeDecoders prototype test
* Fix UIntBuffer
* Fix hard-coded Element identifier in CSDiag
* Fix up more tests
* Account for flatMap changes
This would just set the NominalTypeDecl's declared type to
ErrorType, which caused problems elsewhere.
Instead, generalize the logic used for AbstractFunctionDecl.
This correctly wires up the GenericTypeParamDecl's archetypes even
if the signature didn't validate, fixing crashes if the generic
parameters of the type are referenced.
