Added support to use pkg shlib-{provides,requires} objects.

This effectively checks that all pkgs in a transaction to be installed
or updated, have not unmatched shared libraries, which might happen with
pkgs that had major soname bumps.

This implementation slow downs xbps_transaction_prepare() 2x, due to
the use of xbps_pkgdb_get_pkg_metadata(). A new pkgdb format is required
that adds the pkg shlib-provides objects to pkgdb, avoiding the need
to use xbps_pkgdb_get_pkg_metadata().

lib/transaction_dictionary.c

@@ -279,6 +279,9 @@ xbps_transaction_prepare(struct xbps_handle *xhp)
 		xhp->transd = NULL;
 		return rv;
 	}
+	if (xbps_transaction_shlibs(xhp))
+		return ENODEV;
+
 	/*
 	 * Sort package dependencies if necessary.
 	 */