mq: implement log() on dummyui

mq: implement log() on dummyui

Otherwise ui.log() in extensions.py would explode.

--- a/hgext/mq.py	Sat Dec 15 16:24:08 2018 +0900
+++ b/hgext/mq.py	Sat Dec 15 16:52:04 2018 +0900
@@ -139,6 +139,8 @@
     class dummyui(object):
         def debug(self, msg):
             pass
+        def log(self, event, msgfmt, *msgargs, **opts):
+            pass
     stripext = extensions.load(dummyui(), 'strip', '')
 
 strip = stripext.strip