chgserver: add an explicit gc to trigger __del__

SocketServer.ForkingMixIn uses os._exit which will skip all cleanup handlers.
We want to run __del__ to make things like transactions, {ssh,http}peer,
atomictempfile, dirstateguard, etc. work.

This patch adds a "gc.collect()" to trigger __del__. It is helpful for chg
to pass some test cases in test-devel-warnings.t.

hgext/chgserver.py

@@ -42,6 +42,7 b' from __future__ import absolute_import'
 
 import SocketServer
 import errno
+import gc
 import inspect
 import os
 import re
@@ -569,6 +570,9 b' class _requesthandler(SocketServer.Strea'
                 cerr = commandserver.channeledoutput(self.wfile, 'e')
             traceback.print_exc(file=cerr)
             raise
+        finally:
+            # trigger __del__ since ForkingMixIn uses os._exit
+            gc.collect()
 
 def _tempaddress(address):
     return '%s.%d.tmp' % (address, os.getpid())