Fix an assortment of compiler warnings.

A few potential bugs were removed in the process.  Much code cleanup
remains to be done.

srogue/trader.c

@@ -338,7 +338,7 @@ struct cell {
 	char x_pos;
 };
 struct bordercells {
-	char num_pos;			/* number of frontier cells next to you */
+	unsigned char num_pos;	/* number of frontier cells next to you */
 	struct cell conn[4];	/* the y,x position of above cell */
 } mborder;