For when the symlink for a tap already exists and points to the thing we are about to symlink. This can happen, mostly because my code has sucked, but since the filesystem can be edited by the user at whim, it's possible then too.
Fixes:
$ brew tap adamv/alt
...blah blah blah..
$ brew tap josegonzalez/php
...blah blah blah...
Warning: Could not tap josegonzalez/php/php over mxcl/master/php
Where it should be "over adamv/alt/php".
The symlinks taps write to Formula show up in git status, but this trick prevents this. brew-(un)tap maintain a .gitignore in Formula that contains all the symlinks brew-tap creates.
We add the .gitignore to the root .gitignore and TADA! Magic.
