Bash/Git: update to completion script from Git v2.1.2

Haven't updated this for a while, because I don't use Bash any more, but
may as well give it a refresh.
Homebrew: update Brewfile

It's been a while since I took a snapshot of this, so just doing an
update.
Bash/Git: move completion script into subdirectory

Reduce the clutter, and keep it close to the other Bash completion
files.
Bash: remove references to rvm

I stopped using rvm long ago, in favor of rbenv.
Bash: remove unused timeout3 script

It's been unused for over a year now (see 7fd219f5833a53b7e), so out it
goes.