Revert "Fixed .install for cached packages"

This reverts commit 648a82feead2cfbad36810c842649eb5beef8afb.
Fixed opam-admin make to consistently rebuild the archives
+opam archives should be built if any file in the package has been changed, added or removed
(we could exclude changes to the opam and descr files, but do we care ?)
Closes #868, #874, #879 (together with the revert of the temporary fix)
Merge pull request #883 from AltGr/fix-mk-repo

Fixing opam-admin make to take into account files/ and url modifications and add/remove