Port from Zope 2.7 branch.

After consulting with Mark Hammond, removed the explicit calls to SvcStop().

That method gets invoked automatically by the services framework when a
stop request is generated.  Calling it explicitly too caused the onStop()
method to get called multiple times.  At least ZRS's Service subclasses
have onStop() methods that can't be called multiple times without raising
exceptions (they shut things down, and stuff like sockets go away the
first time onStop() gets called).

lib/python/nt_svcutils/service.py

@@ -234,7 +234,6 @@ class Service(win32serviceutil.ServiceFramework):
                                                win32event.INFINITE)
         if rc == win32event.WAIT_OBJECT_0:
             # user sent a stop service request
-            self.SvcStop()
             keep_running = False
         elif rc == win32event.WAIT_OBJECT_0 + 1:
             # user did not send a service stop request, but
@@ -261,7 +260,6 @@ class Service(win32serviceutil.ServiceFramework):
         # this was an abormal shutdown.
         if self.backoff_cumulative > BACKOFF_MAX:
             self.error("restarting too frequently; quit")
-            self.SvcStop()
             return False
         self.warning("sleep %s to avoid rapid restarts"
                      % self.backoff_interval)