Use uutils-coreutils instead of aardvark_shell_utils

[Atry]

uutils-coreutils is a new alternative to GNU's coreutils. It is better maintained than aardvark_shell_utils. Similar to aardvark_shell_utils, uutils-coreutils does not conflict with md5sha1sum.

[fredemmott]

I think we should be trying for GNU coreutils first, then investigate alternatives:

• it's the defacto standard
• uutils is v0.0.12 - it has not yet had a stable release
• it reduces the difference between our mac and linux environments, likely decreasing the amount of portability issues we have in the long term