Fix compiler warnings.

src/dungeon.c

@@ -2409,7 +2409,8 @@ recalc_mapseen()
     struct monst *mtmp;
     struct cemetery *bp, **bonesaddr;
     unsigned i, ridx;
-    int x, y, ltyp, count, atmp;
+    int x, y, ltyp, count;
+    unsigned int atmp;
 
     /* Should not happen in general, but possible if in the process
      * of being booted from the quest.  The mapseen object gets

src/sp_lev.c

@@ -3763,7 +3763,7 @@ struct opvar *mc;
 {
     int x, y;
     schar mapc;
-    xchar lit;
+    uchar lit;
     struct opvar *ret = selection_opvar((char *) 0);
 
     if (!ov || !mc || !ret)