Windows paths need improved handling

[alexcrichton]

Due to the \ character, windows paths are both invalid URLs as well as causing all the tests to fail on windows. This can be closed when we no longer jankily replace \ with / and also when the tests pass on windows.

[alexcrichton]

One blocker for this issue is dealing with rust-lang/rust#15149

[jhasse]

I'm still getting an error which seems related to \ on Windows:

~/git/rust-opengl-test (master=) cargo build
    Updating git repository `https://github.com/bjz/gl-rs.git`
fatal: '/home/jhasse/.cargo/git/checkouts/gl-rs-1669fe424cfaeccd/C:\msys64\home\jhasse\.cargo\git\db\gl-rs-1669fe424cfaeccd' does not appear to be a git repository
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
Unable to update https://github.com/bjz/gl-rs.git

To learn more, run the command again with --verbose.

~/git/rust-opengl-test (master=)

Should I open a new issue?

[alexcrichton]

Yes please! A small repo to reproduce would also be much appreciated!