X wcfs: mkdir /tmp/wcfs with sticky bit

So that multiple users can create things inside.

wcfs/__init__.py

@@ -63,7 +63,7 @@ The following environment variables can be used to control wcfs.py client:
 
 from __future__ import print_function, absolute_import
 
-import os, sys, hashlib, tempfile, subprocess, time
+import os, sys, hashlib, tempfile, subprocess, time, stat
 import logging as log
 from os.path import dirname
 from errno import ENOENT, EEXIST
@@ -295,18 +295,24 @@ def _wcfs_exe():
 def _mntpt_4zurl(zurl):
     m = hashlib.sha1()
     m.update(zurl)
-    mntpt = "%s/wcfs/%s" % (tempfile.gettempdir(), m.hexdigest())
+    # mkdir /tmp/wcfs with stiky bit. This way multiple users can create subdirectories inside.
+    wcfsroot = "%s/wcfs" % (tempfile.gettempdir())
+    if _mkdir_p(wcfsroot):
+        os.chmod(wcfsroot, 0777 | stat.S_ISVTX)
+    mntpt = "%s/%s" % (wcfsroot, m.hexdigest())
     _mkdir_p(mntpt)
     return mntpt
 
 
 # mkdir -p.
-def _mkdir_p(path):
+def _mkdir_p(path, mode=0777): # -> created(bool)
     try:
-        os.makedirs(path)
+        os.makedirs(path, mode)
     except OSError as e:
         if e.errno != EEXIST:
             raise
+        return False
+    return True
 
 
 # serve starts and runs wcfs server for ZODB @ zurl.