Do not send signals from the master process to parent on shutdown.

Revision 11330 has a nasty side-effect: When running in non-daemon
mode, Squid sends SIGUSR1 signal to the parent process on shutdown.
This results in shell (at least zsh) exit when Squid is interrupted
with C-c. The patch adds a check to prevent the master process from
killing it's parent on shut down.

Same check added for the kill-parent hack.

=== modified file 'src/main.cc'
--- src/main.cc	2011-03-30 19:39:14 +0000
+++ src/main.cc	2011-03-30 19:59:19 +0000
@@ -600,51 +600,51 @@ reconfigure(int sig)
 
     signal(sig, reconfigure);
 #endif
 #endif
 }
 
 void
 shut_down(int sig)
 {
     do_shutdown = sig == SIGINT ? -1 : 1;
     ShutdownSignal = sig;
 #ifdef SIGTTIN
 
     if (SIGTTIN == sig)
         shutdown_status = 1;
 
 #endif
 
     const pid_t ppid = getppid();
 
-    if (ppid > 1) {
+    if (!IamMasterProcess() && ppid > 1) {
         // notify master that we are shutting down
         if (kill(ppid, SIGUSR1) < 0)
             debugs(1, DBG_IMPORTANT, "Failed to send SIGUSR1 to master process,"
                    " pid " << ppid << ": " << xstrerror());
     }
 
 #ifndef _SQUID_MSWIN_
 #if KILL_PARENT_OPT
 
-    if (ppid > 1) {
+    if (!IamMasterProcess() && ppid > 1) {
         debugs(1, DBG_IMPORTANT, "Killing master process, pid " << ppid);
 
         if (kill(ppid, sig) < 0)
             debugs(1, DBG_IMPORTANT, "kill " << ppid << ": " << xstrerror());
     }
 
 #endif /* KILL_PARENT_OPT */
 #if SA_RESETHAND == 0
     signal(SIGTERM, SIG_DFL);
 
     signal(SIGINT, SIG_DFL);
 
 #endif
 #endif
 }
 
 static void
 serverConnectionsOpen(void)
 {
     if (IamPrimaryProcess()) {