Made conky eval useful

Conky's eval seems rather useless, at least I couldn't get it do anything I wanted, so I added a little patch to make it more useful (to me):

diff --git a/src/conky.c b/src/conky.c
index 5848b61..8702cea 100644
--- a/src/conky.c
+++ b/src/conky.c
@@ -1103,7 +1103,9 @@ void generate_text_internal(char *p, int p_max_size,
 #endif /* IMLIB2 */
 			OBJ(eval) {
-				evaluate(obj->data.s, p, p_max_size);
+				char buffer[max_user_text];
+				evaluate(obj->data.s, buffer, sizeof(buffer));
+				evaluate(buffer, p, p_max_size);
 			OBJ(exec) {
 				print_exec(obj, p, p_max_size);

Probably not the best thing ever, but seems to do the trick for me; now I can get the address of the interface connected to the big bad internets with (note: won't work correctly when multiple interfaces with default route):

${eval $${addr ${gw_iface}}}

The patch applies against conky 1.9.0, unfortunately not against the heavily rewritten git master.

Update: similar patch I made against the 1.10.x has been merged to upstream conky; yay!