Use int instead of long for money

Code dealing with money mixes int and long pretty haphazardly.
Harmless, because practical amounts of money fit into int on any
machine capable of running the server.  Clean up anyway.

include/loan.h

@@ -52,8 +52,8 @@ struct lonstr {
     signed char l_status;	/* loan status */
     int l_irate;		/* interest rate */
     int l_ldur;			/* intended duration */
-    long l_amtpaid;		/* amount paid so far */
-    long l_amtdue;		/* amount still owed */
+    int l_amtpaid;		/* amount paid so far */
+    int l_amtdue;		/* amount still owed */
     time_t l_lastpay;		/* date of most recent payment */
     time_t l_duedate;		/* date after which interest doubles, etc */
 };