Level temperature

Allow setting a per-level "temperature": hot, cold, or temperate
via special level flags. Currently it only affects some messages
in Gehennom, but it could be expanded to ice melting, water freezing,
or monster generation, for example.

Invalidates saves and bones.

include/patchlevel.h

@@ -17,7 +17,7 @@
  * Incrementing EDITLEVEL can be used to force invalidation of old bones
  * and save files.
  */
-#define EDITLEVEL 69
+#define EDITLEVEL 70
 
 /*
  * Development status possibilities.