libxbps: improve code to match replaced package patterns.

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.

lib/transaction_dictionary.c

@@ -235,6 +235,15 @@ xbps_transaction_prepare(void)
 		errno = ENODEV;
 		return NULL;
 	}
+	/*
+	 * Check for packages to be replaced.
+	 */
+	if ((rv = xbps_transaction_package_replace(transd)) != 0) {
+		errno = rv;
+		prop_object_release(transd);
+		prop_object_release(trans_mdeps);
+		return NULL;
+	}
 	/*
 	 * Sort package dependencies if necessary.
 	 */