When type-checking a slice type, "desugar" it to a type that is

generic over the type of the base.  By "generic" I mean that it's
looked up by prepending the word "Slice" to the name of the base
type.

Swift SVN r1464

lib/Parse/ParsePattern.cpp

@@ -47,6 +47,9 @@ static bool checkFullyTyped(Parser &P, Type type) {
   case TypeKind::Array:
     return checkFullyTyped(P, cast<ArrayType>(type)->getBaseType());
 
+  case TypeKind::ArraySlice:
+    return checkFullyTyped(P, cast<ArraySliceType>(type)->getBaseType());
+
   case TypeKind::Function: {
     FunctionType *fn = cast<FunctionType>(type);
     return checkFullyTyped(P, fn->getInput())