Add quilt integration for packages

make package/<package>-prepare QUILT=1 will apply all patches using quilt
Autorebuild will be disabled, so that you can edit all patches in the build dir.
When you're done editing patches and everything works, you can call:
make package/<package>-refresh
That will copy the updated patches from quilt into package/<package>/patches,
and remove all old patches.
Before the patches are overwritten, the correct order of the patches is verified
('cat series' is compared against 'sort series').

SVN-Revision: 7471