expand: re-add slash conversion to globbing

When we removed all uses of filepath.Join and thus filepath.Clean, we
forgot that Clean also performs FromSlash. We need that piece, because
we want globbing with forward slashes to work on Windows too.

This is useful so that a unix-like script with globbing also works on
Windows. There's no reason not to do that, since slashes are forbidden
from Windows file and directory names, anyway.

The regression was introduced in the previous commit, and is now fixed.

expand/expand.go

@@ -621,8 +621,11 @@ func pathJoin2(elem1, elem2 string) string {
 	return elem1 + string(filepath.Separator) + elem2
 }
 
-// pathSplit is the opposite of pathJoin.
+// pathSplit splits a file path into its elements, retaining empty ones. Before
+// splitting, slashes are replaced with filepath.Separator, so that splitting
+// Unix paths on Windows works as well.
 func pathSplit(path string) []string {
+	path = filepath.FromSlash(path)
 	return strings.Split(path, string(filepath.Separator))
 }