[QBS] Re-do the wildcard implementation.

[Bornemann Joerg]

> So the pattern "src/**/*.cpp" will handle _all_ "*.cpp" files in "src" and all subdirectories of "src", I think this semantic is rather clear and, as we see, it's easy to be documented.

Yes, if ** is just meant as a flag, it's easy.
Would this be allowed: "artwork/**/subdir/*.jpg"?
And what does it expand to?

> As additional bonus with this flag we can use both recursive and non-recursive targets in one Groups, which can simplify qbs-based build scripts.

That's definitely a point on my pro list.


Cheers,

Jörg