[PATCH] ui: improve docs on ui.log

[Augie Fackler]

# HG changeset patch
# User Augie Fackler <augie at google.com>
# Date 1441896603 14400
#      Thu Sep 10 10:50:03 2015 -0400
# Node ID 18fd6b809fe39b25f7525cf7019f58aaecd8dad5
# Parent  a4da463df6cf0d0bcf36afa478ed18d1c818ff3e
ui: improve docs on ui.log

This makes the documentation on ui.log line up with the use of that
interface in blackbox.

diff --git a/mercurial/ui.py b/mercurial/ui.py
--- a/mercurial/ui.py
+++ b/mercurial/ui.py
@@ -969,9 +969,12 @@ class ui(object):
 
         service should be a readily-identifiable subsystem, which will
         allow filtering.
-        message should be a newline-terminated string to log.
+
+        *msg should be a newline-terminated format string to log, and
+        then any values to %-format into that format string.
+
+        **opts currently has no defined meanings.
         '''
-        pass
 
     def label(self, msg, label):
         '''style msg based on supplied label