Fix coloring madness in depot_tools.

'setup_color' now contains logic to correctly detect:
  * cmd
  * cmd pipe
  * msys bash
  * msys pipe
  * cmd running inside msys bash (git-command)
  * cmd pipe running inside msys bash (git-command > outfile)

R=brucedawson@chromium.org, dnj@chromium.org
BUG=600049

Review URL: https://codereview.chromium.org/1851283002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@299682 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/git_common.py b/git_common.py
index 949ba46..bef628e 100644
--- a/git_common.py
+++ b/git_common.py
@@ -22,6 +22,7 @@
 import logging
 import os
 import re
+import setup_color
 import shutil
 import signal
 import sys
@@ -281,7 +282,7 @@
 ## Git functions
 
 
-def blame(filename, revision=None, porcelain=False, *args):
+def blame(filename, revision=None, porcelain=False, *_args):
   command = ['blame']
   if porcelain:
     command.append('-p')
@@ -576,7 +577,7 @@
   Automatically checks if sys.stdout is a non-TTY stream. If so, it avoids
   running less and just yields sys.stdout.
   """
-  if not sys.stdout.isatty():
+  if not setup_color.IS_TTY:
     yield sys.stdout
     return