pip_generate_wrapper: 'invalid cross-device link' error when /tmp and target directory aren't on the same partition.

[gfl-chris]

Encountering the above error when running pip_generate_wrapper. I believe it's due to the fact that my home directory is mounted on a different partition.

I fixed the issue here based on the code from here.

[joshburkart]

Cool! Send PR? (Although @evanj hasn't been responsive lately so we might want to fork this into an official project...)

[therc]

It should be OK to fork the project: #54 (comment)

[evanj]

Yes please fork it somewhere; I would be happy to accept a PR to post a big note in the README.md!