obsolete: make sure windows tests pass when stat() is given a URL This is a temporary fix for an issue that's only visible on windows, but exists on other platforms as well. The issue is if we're trying to use obsstore from a remote peer and that peer is a static HTTP repo, vfs tries to os.stat() a remote file using a URL to that file (e.g. http://localhost/repo/.hg/store/obsstore). The next patch in this series makes branchcache obsolescence-aware, so in certain situations exchange process will try os.stat()ing a URL. On windows this will produce an OSError that is not ENOENT, but EINVAL instead (because of `:` symbol, for example). Differential Revision: https://phab.mercurial-scm.org/D12100