rogue3: replace alarm() calls with a portable function.

Calls to alarm() in main.c are replaced with md_start_checkout_timer(),
so the #ifdefs around nonportable code can be confined to mdport.c.

rogue3/mdport.c

@@ -1510,11 +1510,10 @@ md_tstpsignal(void)
 #endif
 }
 
-#if defined(CHECKTIME)
 void
 md_start_checkout_timer(int time)
 {
-    int  checkout();
+    void checkout();
 
 #if defined(HAVE_ALARM) && defined(SIGALRM)
     signal(SIGALRM, checkout);
@@ -1529,7 +1528,6 @@ md_stop_checkout_timer(void)
     signal(SIGALRM, SIG_IGN);
 #endif
 }
-#endif
 
 long
 md_memused()