Fix renaming of .tmp files on Windows

On Windows, you can't rename over a file that exists, and you can't
delete a file you stil have open.

Signed-off-by: Paul "TBBle" Hampson <Paul.Hampson@Pobox.com>

utils/format.py

@@ -197,6 +197,7 @@ def process(md_path, signatures_to_update):
     else:
         with open(md_path + ".tmp", "wt") as f:
             f.write(out)
+        os.unlink(md_path)
         os.rename(md_path + ".tmp", md_path)
 
     # Legacy
@@ -214,7 +215,8 @@ def process(md_path, signatures_to_update):
         else:
             with open(md_legacy_path + ".tmp", "wt") as f:
                 f.write(out_legacy)
-                os.rename(md_legacy_path + ".tmp", md_legacy_path)
+            os.unlink(md_legacy_path)
+            os.rename(md_legacy_path + ".tmp", md_legacy_path)
 
     # Historic