Add comment explaining why we access the filesystem via Path objects in glob selectors

Author: barneygale

Lib/pathlib.py

@@ -349,6 +349,10 @@ def __init__(self, pat, child_parts, flavour):
 
     def _select_from(self, parent_path, is_dir, exists):
         try:
+            # bpo-24132: a future version of pathlib will support subclassing
+            # of pathlib.Path to customize how the filesystem is accessed. We
+            # must honour those customizations here, rather than calling
+            # os.scandir() directly.
             with parent_path._scandir() as scandir_it:
                 entries = list(scandir_it)
             for entry in entries: