API update for subprojects with resources

[Nicola Pero]

If you have subprojects with resources, you need to update your
GNUmakefile.

Now you need to have

xxx_HAS_RESOURCE_BUNDLE = yes

in the GNUmakefile in order for gnustep-make to turn on the resource
bundle code.

The existing API/code was buggy, in that it was creating the Resources/
directory [and destroying it as well!] even if no resource bundle was used
[bug originally reported by Helge a 'few' months ago].

Anyway, if you add

xxx_HAS_RESOURCE_BUNDLE = yes

everything will work both with the old and the new gnustep-make, so it's
not a big problem.