Fix t5516 on cygwin: it does not like double slashes at the beginning of a path
The double slashes "//" result from url./$TRASH/. expansion and the current directory, which even in cygwin contains "/" as first character. In cygwin such strings have special meaning: UNC path. Accessing an UNC path built for test purpose usually fails.
Signed-off-by: Alex Riesen <email@example.com> Signed-off-by: Junio C Hamano <firstname.lastname@example.org>