lfs: special case the null:// usercache instead of treating it as a url The previous code worked on Windows, but not on Unix, and a pending patch's test failed. The url being used was something like "/tmp/.../client1/null://", courtesy of ui.configpath(). Looking at the doc comment, this seems like it's maybe not the right function to call (why should a relative cache path be expanded relative to the repo root or config file?), but largefiles has been using it since 8b8dd13295db (Oct 2011). It was introduced in 1b591f9b7fd2 (Jan 2011) without comment or callers. A grep over the whole history shows that only largefiles used it until lfs and infinitepush came along recently. It looks like if the `if not os.path.isabs(v) or "://" not in v` in configpath() is changed to an 'and', both Linux and Windows are happy. I'm guessing that "://" is to pick off URLs, so that seems reasonable. But I'm not sure why it isn't explicitly "file://", and I thought that "file://foo" is relative anyway. (At least, there are doctests for file:///tmp in util.url.) There is no mention of this setting in the help, but it is referenced on the wiki page for largefiles. (There's no mention that this is intended to be a URL, and the example uses an absolute path.) I don't want this blocking the rest of the lfs server discovery stuff. It was also wrong to allow a file:// URL here, but not in largefiles.