resolve symlinks in local files

[ptone]

this allows --find-links to point to a local folder of symlinks to valid archives

the tar libraries choke when checking valid
filenames because they don't resolve symlinks

[hltbra]

Hi,

I do not understand very well the problem. Could you please show me a scenario where the problem happens?

[ptone]

The scenario where I hit this was in the first attempt to make use of the download cache as a --find-links target.

Because all the download cache is full of archives named as quoted URLs, they won't work. So I put together a quick script that just symlinked django-1.3.tar.gz in a folder to /http%2adblahblahblahdjango-1.3.tar.gz

pip will recognize the symlink as a valid archive, but when it goes to check the contents with the python tarfile lib, that library chokes on the symlink and pip will error out of the install. This change simply resolves the symlink before handing it off to the rest of the installation process.

[ptone]

Note I have since developed another way of using the download cache as a --find-link target, but figured this small fix was worth its own pull. I'll submit the more built in approach in its own pull shortly