Allow type checking qualified references to generic nominals with free type

variables

This change allows the type checker to create member references to generic
nominals with free type variables -- see tests.  This is important for code
completion, for example, swift.Dictionary.#^A^#

Fixes rdar://15980316


Swift SVN r14461

lib/AST/Decl.cpp

@@ -650,6 +650,8 @@ void ValueDecl::overwriteType(Type T) {
 DeclContext *ValueDecl::getPotentialGenericDeclContext() {
   if (auto func = dyn_cast<AbstractFunctionDecl>(this))
     return func;
+  if (auto NTD = dyn_cast<NominalTypeDecl>(this))
+    return NTD;
 
   return getDeclContext();
 }