windows: use abspath in the git extension

We replace `os.path.abspath` with `util.abspath`. This should solve more "drive
capitalization" issue on Windows.

Differential Revision: https://phab.mercurial-scm.org/D11068

hgext/git/__init__.py

@@ -284,7 +284,7 b' class gitbmstore(object):'
 
 def init(orig, ui, dest=b'.', **opts):
     if opts.get('git', False):
-        path = os.path.abspath(dest)
+        path = util.abspath(dest)
         # TODO: walk up looking for the git repo
         _setupdothg(ui, path)
         return 0