Fix for 3141: symlink in consolescript path

[AvdN]

This fixes issue #3141, where a uninstall error occurs
when upgrading/uninstalling and the path to the console
script contains symlinks. As the path is in installed-files.txt
as well and these paths are joined to the real path coming
from .egg_info, the uninstall will try to remove the
console script using two different paths and fail on the second
(non-real) path.

[xavfernandez]

Since we dont want to break it for #2552, I think a middle-ground solution could be:

         if config.has_section('console_scripts'):
             if dist_in_usersite(dist):
                 bin_dir = bin_user
             else:
                 bin_dir = bin_py
             bin_dir = normalize_path(bin_dir)
             for name, value in config.items('console_scripts'):         
                 paths_to_remove.add(os.path.join(bin_dir, name))

[xavfernandez]

cc @qwcode since you reviewed and merged #2552
An alternate solution is mathieulongtin@4dd0ab2 which I like less.

[qwcode]

I think I'd rather have this fix: https://github.com/qwcode/pip/commit/e2450f0e99d8d94e72ea746f34f0cf1e5c51b7dd

this places the fix closer to the cause of all this (right below it), so I think it's clearer.

also, the point is not to resolve the console scripts I think, but to detect when the set already contains a resolved version of them.

I think my comment in the diff is accurate enough on how this happens, but I'd like to make it clearer tomorrow and add a test, and then I could post a PR.

[xavfernandez]

@qwcode Read and approved :)

[AvdN]

@qwcode I tested your fix ( https://github.com/qwcode/pip/commit/e2450f0e99d8d94e72ea746f34f0cf1e5c51b7dd ) locally here and it solves the issue I am having as well.
Are you going to put that in as a PR? Should I close this PR? I am not partial to any solution, just would like to get rid of the uninstall failure messages ;-)

[qwcode]

@AvdN yea, I'll be putting in a PR. hopefully today. if/when it's merged, I'd go around and cleanup other issues and PRs

[qwcode]

btw, my PR will be different than what I posted above, since after adding tests, I realized it was flawed, but I'll explain more when I post

[qwcode]

closing in lieu of #3154