just-in-time creation for (implicit) Provides

Expecting the worst is easy to code, but has its disadvantages e.g.
by creating package structures which otherwise would have never
existed. By creating the provides instead at the time a package
structure is added we are well prepared for the introduction of partial
architectures, massive amounts of M-A:foreign (and :allowed) and co as
far as provides are concerned at least. We have something relatively
similar for dependencies already.

Many tests are added for both M-A states and the code cleaned to
properly support implicit provides for foreign architectures and
architectures we 'just' happen to parse.

Git-Dch: Ignore