Integrate properly -e URLs

[guyzmo]

I'm using a lot this recipe (to be compatible with the others, and sometimes I'm changing some dependencies to have them point to my fork while a PR is in the stack. but then, collective.recipe.pip looks like it's anyway only resolving the egg part and gets the package from pip, not the fork from git. example:

requirements.txt:

-e https://github.com/foo/bar@HEAD#egg=bar

will download bar from pip, not from github. As a work around I'm updating both the requirements.txt and the buildout.cfg by adding the following rule:

extensions=gp.vcsdevelop
vcs-extend-develop=git+https://github.com/foo/bar#egg=bar

I've seen there's a special treatment made with URLs that contain a #egg= part. But I'm not sure how to exploit that properly…