Move stamp (dependency) files outside the (version specific) source
directories, so other packages can hardcode dependencies on them instead
of having to use <PACKAGE>_VERSION variables.
This is important as the variables in the make rules are evaluated when
the rules is seen, which might be before the dependent makefile is parsed
(and hence <PACKAGE>_VERSION variable is known, screwing up stuff.
The downside of this is that the package isn't automatically rebuilt
when the version changes (E.G. by a svn update) and you now also have to
remove the stamp files next to $(BUILD_DIR)/<PACKAGE>-* to force a rebuild.
Other packages might also support Linux-style out of tree builds
with the O=<dir> syntax (E.G. Busybox does). As make automatically
forwards command line variable definitions those packages get very
confused. Fix this by telling make to not do so
Will need to try to copy eventual pre-existing project-specific deps back
to package/config in order not to mess up the corresponding timestamps (to avoid superfluous rebuilds)..
