Show menu when paying items

... and have more than 1 billed item, and using non-traditional
menustyle.

I opted to add an extra field to the bill struct, because
that made the code cleaner.

Breaks saves and bones.

include/mextra.h

@@ -113,6 +113,7 @@ struct epri {
 struct bill_x {
     unsigned bo_id;
     boolean useup;
+    boolean queuedpay;
     long price; /* price per unit */
     long bquan; /* amount used up */
 };