See the long Note [Binders in Template Haskell] in Convert.lhs
which explains it all.  This patch fixes Trac #5037.

The key change is that NameU binders (ones made up by newName in
Template Haskell, and by TH quotations) now make Exact RdrNames again,
rather than making RdrNames with heavily encoded OccNames like x[03cv].
(This encoding is what was making #5037 fail.)