[Toybox] Grep --color and tests.

[Rob Landley]

On 12/27/18 12:46 PM, enh wrote:
> meh, BSD-based regex implementations seem to think that the empty
> regex is an error anyway. (i only skimmed it, but i think POSIX
> agrees: http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html)

Earlier versions I was catching the empty regex and manually matching the whole
thing, I can do that again. :)

(Some build script somewhere cared, I forget which since I haven't gotten the
LFS/BLFS build environment recreated yet...)

Rob