test: run testcases with POSIX absolute paths on Windows

Some test cases are skipped on Windows by marking with POSIX prereq.
This is because arguments look like absolute paths (such as /a/b)
for regular Windows programs (*.exe executables, no bash scripts)
are changed to Windows paths (like C:/msysgit/a/b).

There is no cygpath nor equivalent on msysGit, but it is easy to
write one. New subcommand "mingw_path" is added in test-path-utils,
so that we can get the expected absolute paths on Windows. E.g.

    COMMAND LINE                        Linux output  Windows output
    ==================================  ============  ===============
    test-path-utils mingw_path /        /             C:/msysgit
    test-path-utils mingw_path /a/b/    /a/b/         C:/msysgit/a/b/

With this utility, most skipped test cases in t0060 can be turned on
to be tested correctly on Windows.

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t0060-path-utils.sh

@@ -8,13 +8,15 @@ test_description='Test various path utilities'
 . ./test-lib.sh
 
 norm_path() {
+	expected=$(test-path-utils mingw_path "$2")
 	test_expect_success $3 "normalize path: $1 => $2" \
-	"test \"\$(test-path-utils normalize_path_copy '$1')\" = '$2'"
+	"test \"\$(test-path-utils normalize_path_copy '$1')\" = '$expected'"
 }
 
 relative_path() {
+	expected=$(test-path-utils mingw_path "$3")
 	test_expect_success $4 "relative path: $1 $2 => $3" \
-	"test \"\$(test-path-utils relative_path '$1' '$2')\" = '$3'"
+	"test \"\$(test-path-utils relative_path '$1' '$2')\" = '$expected'"
 }
 
 # On Windows, we are using MSYS's bash, which mangles the paths.
@@ -39,8 +41,8 @@ ancestor() {
 	 test \"\$actual\" = '$expected'"
 }
 
-# Absolute path tests must be skipped on Windows because due to path mangling
-# the test program never sees a POSIX-style absolute path
+# Some absolute path tests should be skipped on Windows due to path mangling
+# on POSIX-style absolute paths
 case $(uname -s) in
 *MINGW*)
 	;;
@@ -73,30 +75,30 @@ norm_path d1/s1//../s2/../../d2 d2
 norm_path d1/.../d2 d1/.../d2
 norm_path d1/..././../d2 d1/d2
 
-norm_path / / POSIX
+norm_path / /
 norm_path // / POSIX
 norm_path /// / POSIX
-norm_path /. / POSIX
+norm_path /. /
 norm_path /./ / POSIX
 norm_path /./.. ++failed++ POSIX
-norm_path /../. ++failed++ POSIX
+norm_path /../. ++failed++
 norm_path /./../.// ++failed++ POSIX
 norm_path /dir/.. / POSIX
 norm_path /dir/sub/../.. / POSIX
 norm_path /dir/sub/../../.. ++failed++ POSIX
-norm_path /dir /dir POSIX
-norm_path /dir// /dir/ POSIX
-norm_path /./dir /dir POSIX
-norm_path /dir/. /dir/ POSIX
-norm_path /dir///./ /dir/ POSIX
-norm_path /dir//sub/.. /dir/ POSIX
-norm_path /dir/sub/../ /dir/ POSIX
+norm_path /dir /dir
+norm_path /dir// /dir/
+norm_path /./dir /dir
+norm_path /dir/. /dir/
+norm_path /dir///./ /dir/
+norm_path /dir//sub/.. /dir/
+norm_path /dir/sub/../ /dir/
 norm_path //dir/sub/../. /dir/ POSIX
-norm_path /dir/s1/../s2/ /dir/s2/ POSIX
-norm_path /d1/s1///s2/..//../s3/ /d1/s3/ POSIX
-norm_path /d1/s1//../s2/../../d2 /d2 POSIX
-norm_path /d1/.../d2 /d1/.../d2 POSIX
-norm_path /d1/..././../d2 /d1/d2 POSIX
+norm_path /dir/s1/../s2/ /dir/s2/
+norm_path /d1/s1///s2/..//../s3/ /d1/s3/
+norm_path /d1/s1//../s2/../../d2 /d2
+norm_path /d1/.../d2 /d1/.../d2
+norm_path /d1/..././../d2 /d1/d2
 
 ancestor / / -1
 ancestor /foo / 0
@@ -198,8 +200,8 @@ relative_path /		/a/b/		../../
 relative_path /a/c	/a/b/		../c
 relative_path /a/c	/a/b		../c
 relative_path /x/y	/a/b/		../../x/y
-relative_path /a/b	"<empty>"	/a/b	POSIX
-relative_path /a/b 	"<null>"	/a/b	POSIX
+relative_path /a/b	"<empty>"	/a/b
+relative_path /a/b 	"<null>"	/a/b
 relative_path a/b/c/	a/b/		c/
 relative_path a/b/c/	a/b		c/
 relative_path a/b//c	a//b		c

test-path-utils.c

@@ -116,6 +116,11 @@ int main(int argc, char **argv)
 		return 0;
 	}
 
+	if (argc == 3 && !strcmp(argv[1], "mingw_path")) {
+		puts(argv[2]);
+		return 0;
+	}
+
 	if (argc == 4 && !strcmp(argv[1], "relative_path")) {
 		struct strbuf sb = STRBUF_INIT;
 		const char *in, *prefix, *rel;