Properly comment about shutdown process in init.cpp file

Author: wraith7

src/init.cpp

@@ -102,12 +102,11 @@ static const char* FEE_ESTIMATES_FILENAME="fee_estimates.dat";
 // created by AppInit() or the Qt main() function.
 //
 // A clean exit happens when StartShutdown() or the SIGTERM
-// signal handler sets fRequestShutdown, which triggers
-// the DetectShutdownThread(), which interrupts the main thread group.
-// DetectShutdownThread() then exits, which causes AppInit() to
-// continue (it .joins the shutdown thread).
-// Shutdown() is then
-// called to clean up database connections, and stop other
+// signal handler sets fRequestShutdown, which makes main thread's
+// WaitForShutdown() interrupts the thread group.
+// And then, WaitForShutdown() makes all other on-going threads
+// in the thread group join the main thread.
+// Shutdown() is then called to clean up database connections, and stop other
 // threads that should only be stopped after the main network-processing
 // threads have exited.
 //