Add path package

For testing purposes we need to get the long path of filesystem paths
on Windows machines. By default non-UTF8 syscalls will return the short path
(Ex:"C:\PROGRA~1" instead of "C:\Program Files"). This package exports
previously private functions used in the symlink package to determine the
long path of a file/directory.
Ah, I see. The underlying problem seems to be that os.TempDir calls GetTempPathW
which can return a short-form path.

I'd suggest that this package is not really a primitive we want to be providing.
How about something that solves the exact issue you have instead of adding this?

Would you be able to use os.SameFile to solve the same problem (open
both paths and check that they point to the same thing?)

Or if that's not possible, a primitive in github.com/juju/testing/checkers,
say SamePath that checks whether two paths are actually equal?

Either way, creating a package that can be only used under Windows, forcing
test code to be Windows-specific too, does not seem like a great way forward.