The InternedString change conflicted with Travis's keyword-params change,
since the arg names were switched to InternedStrings.

I decided to not intern the param names any more, and instead represent them
as llvm::StringRef.  Another option would be to intern the builtin ones, even
though there's no independent benefit to doing so, since that would let us use
InternedStrings more generally.  Probably the "best" but most complicated would
be to have the StringRef version and then an InternedString version as well
that was constructed when needed.