Deprecate git-flow and use git-flow-avh instead

[Anahkiasen]

This is not a bug per se and I'm not entirely sure this is the correct repository so bear with me. Currently when you do brew install git-flow it'll install this version which has been abandonned for more than 4 years, the correct version (ie. what most people actually mean to install) is located under the git-flow-avh formula.

Now most people do not know this nor notice it, there is no warning or anything. This issue is to open a discussion in favor (or not) of removing the old git-flow formula and rename the git-flow-avh formula in its place.

Again, I'm not sure if there's ever been a similar situation in Homebrew and what the correct procedure is. The contributing guidelines do not mention deprecated formulas and considering the old repository is abandoned there is little hope for an issue opened there to have any effect.

cc @petervanderdoes

[MikeMcQuaid]

If you can convince nvie to officially deprecate https://github.com/nvie/gitflow and point to git-flow-avh then we'll consider it. Otherwise, we're going to fall back to the relative upstream names.

[Anahkiasen]

I understand, I sent an email to nvie, will see what he thinks