Fixed bug whereby interrupt 0 = interrupt/alarm, i.e., SIGALRM, wasn't

being switched over from default handling (which is process termination)
to S48/scsh handling.

scsh/sighandlers1.c

@@ -175,7 +175,7 @@ void install_scsh_handlers(void)
   new.sa_flags = 0;
 
   for(i=max_sig; i>=0; i--)
-    if( sig2int[i] ) {
+    if( sig2int[i] >= 0 ) {
       /* This is a signal we want the S48 interrupt system to handle. */
       sigaction(i, &new, 0);
       }