There's no need to prop_dictionary_copy the returned dictionary to
later have to free it again, just return directly the dictionary and
avoid the free(3)s.
1- We can cache the result of the first xbps_pkgdb_init() when it fails
and avoid the malloc/free/access from it.
2- We cache the uname(2) result into a private var in xbps_handle and
use it in xbps_pkg_arch_match().
This improves performance by ~5% approx and it's close as it was before
introducing the repository index format 1.5.
The replaces code now checks all package dictionaries in the
transaction dictionary, and the sorting algorithm will put packages
to be removed at the head of the tailq.
This should fix issue 11 in googlecode.
