mingw (t5580): document bug when cloning from backslashed UNC paths
Due to a quirk in Git's method to spawn git-upload-pack, there is a
problem when passing paths with backslashes in them: Git will force the
command-line through the shell, which has different quoting semantics in
Git for Windows (being an MSYS2 program) than regular Win32 executables
such as git.exe itself.
The symptom is that the first of the two backslashes in UNC paths of the
form \\myserver\folder\repository.git is *stripped off*.
Document this bug by introducing a test case.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>