revert set-profiles to unmerge-profiles and merge-profiles

Hi, Alexander.

You changed from `(unmerge-profiles [:dev]) (merge-profiles [:release])` to `(set-profiles [:release] [:dev]) ` at c8b06e0ff14fa85dd4d65865a1e19cc36256f2a5 .
But it causes to disable to `lein with-profiles ...` function at release time.
Because, `unmerge-profiles` and `merge-profiles` cared `with-profiles` profiles, but `set-profiles` not care `with-profiles` profiles.
(See https://github.com/technomancy/leiningen/blob/master/leiningen-core/src/leiningen/core/project.clj#L612 . `merge-profiles` and `unmerge-profiles` includes `(concat included-profiles profiles)`, but `set-profiles` not includes this code.)

I need to `with-profiles` for to change some environments. Will you be so obliging as to see this problem.