Stinking clouds block line of sight

... you will also get a message when a seen stinking cloud
or the one surrounding the hero dissipates.

Original feature comes from Fourk, but this version (with some
minor changes) comes from xnethack by copperwater <aosdict@gmail.com>

src/decl.c

@@ -577,6 +577,8 @@ const struct instance_globals g_init = {
     NULL, /* regions */
     0, /* n_regions */
     0, /* max_regions */
+    FALSE, /* gas_cloud_diss_within */
+    0, /* gas_cloud_diss_seen */
 
     /* restore.c */
     0, /* n_ids_mapped */