[PATCH] cmdutil: use isstdiofilename() where appropriate

[Yuya Nishihara]

# HG changeset patch
# User Yuya Nishihara <yuya at tcha.org>
# Date 1496326103 -32400
#      Thu Jun 01 23:08:23 2017 +0900
# Node ID fbc9705beb0eb803e6efd2234fcb1de6ffb358de
# Parent  ee0119499321b4b1df8e04694d82f6ca425e60df
cmdutil: use isstdiofilename() where appropriate

diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -493,7 +493,7 @@ def logmessage(ui, opts):
                            'exclusive'))
     if not message and logfile:
         try:
-            if logfile == '-':
+            if isstdiofilename(logfile):
                 message = ui.fin.read()
             else:
                 message = '\n'.join(util.readfile(logfile).splitlines())