submodules: fix ambiguous absolute paths under Windows

Under Windows the "git rev-parse --git-dir" and "pwd" commands may return
either drive-letter-colon or POSIX style paths. This makes module_clone()
behave badly because it expects absolute paths to always start with a '/'.

Fix that by always converting the "c:/" notation into "/c/" when computing
the relative paths from gitdir to the submodule work tree and back.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-submodule.sh

@@ -151,6 +151,9 @@ module_clone()
 
 	a=$(cd "$gitdir" && pwd)/
 	b=$(cd "$path" && pwd)/
+	# normalize Windows-style absolute paths to POSIX-style absolute paths
+	case $a in [a-zA-Z]:/*) a=/${a%%:*}${a#*:} ;; esac
+	case $b in [a-zA-Z]:/*) b=/${b%%:*}${b#*:} ;; esac
 	# Remove all common leading directories after a sanity check
 	if test "${a#$b}" != "$a" || test "${b#$a}" != "$b"; then
 		die "$(eval_gettext "Gitdir '\$a' is part of the submodule path '\$b' or vice versa")"