Futureproofing hypothetical type mismatches

If we ever want huge maps with COLNO or ROWNO larger than signed char,
this will at least allow the game to compile and start when typedef'ing
xchar to int. Trying to use huge maps exposes more bugs.

include/patchlevel.h

@@ -17,7 +17,7 @@
  * Incrementing EDITLEVEL can be used to force invalidation of old bones
  * and save files.
  */
-#define EDITLEVEL 25
+#define EDITLEVEL 26
 
 /*
  * Development status possibilities.