Unused case.

I just realized that existential quantifiers should never appear in the
left-hand-side of a subtraction. The implementation seems to agree with that.
Merge remote-tracking branch 'refs/remotes/origin/master'
Merge branch 'jonathan'
Further fixes to the install: target; add uninstall:.
More work on the configure script.
More work on the configure script.
(Failed) attempt to separate the ocamlbuild rules into a separate file.