Skip Test on Windows

Currently renaming files is not supported while the the OS doesn't support renaming open files.
When closing the file, as done in the code by using http://smmap.readthedocs.io/en/latest/api.html#smmap.mman.StaticWindowMapManager.force_map_handle_removal_win force_map_handle_removal_win, we can rename, but the cache does still have a handle to this file and crashes.

Author: stuertz

gitdb/test/db/test_pack.py

@@ -10,13 +10,17 @@
 from gitdb.db import PackedDB
 
 from gitdb.exc import BadObject, AmbiguousObjectName
+from gitdb.util import mman
 
 import os
 import random
+import sys
 
+from unittest import skipIf
 
 class TestPackDB(TestDBBase):
 
+    @skipIf(sys.platform == "win32", "not supported on windows currently")
     @with_rw_directory
     @with_packs_rw
     def test_writing(self, path):
@@ -30,6 +34,11 @@ def test_writing(self, path):
         # packs removed - rename a file, should affect the glob
         pack_path = pdb.entities()[0].pack().path()
         new_pack_path = pack_path + "renamed"
+        if sys.platform == "win32":
+            # This is just the beginning: While using thsi function, we are not
+            # allowed to have any handle to thsi path, which is currently not
+            # the case. The pack caching does have a handle :-(
+            mman.force_map_handle_removal_win(pack_path)
         os.rename(pack_path, new_pack_path)
 
         pdb.update_cache(force=True)