tests/test-issue433

color: add --color switch

--color works like GNU grep --color. --color=auto only colorizes output
for non-dumb terminals that are TTYs.

#!/bin/sh
# http://www.selenic.com/mercurial/bts/issue433

hg init a
cd a
echo a > a
hg commit -Ama

hg parents -r 0 doesnotexist
true