[packagekit] Backend developers, new function

[Daniel Nicoletti]

Hi all,
I've just pushed a pk_backend_get_provides() function
to allow frontends to know beforehand about what
does the backend support, I've added the method
to some backends (aptcc, zif, zypp), but I wasn't sure
about all of them and the code might be wrong for
your backend, so please take a look/update it.

Best,

--
Daniel Nicoletti

KDE Developer - http://dantti.wordpress.com