'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