grep: Only use --color on git 1.6.3 and later

The --color flag wasn't introduced until git 1.6.3.  Prior to that
version, `git grep --color` just produces a fatal error, as it is
an unsupported option.  Since this is just pretty output and is not
critical to execution, we can simply omit the option if the version
of git we are running on doesn't support it.

Signed-off-by: Shawn O. Pearce <sop@google.com>
1 file changed