windows: use abspath in commandserver
We replace `os.path.abspath` with `util.abspath`. This should solve more "drive
capitalization" issue on Windows.
Differential Revision: https://phab.mercurial-scm.org/D11061
== New Features ==
* `hg config` now has a `--source` option to show where each
configuration value comes from.
== Default Format Change ==
These changes affects newly created repositories (or new clone) done with
Mercurial 5.8.
== New Experimental Features ==
== Bug Fixes ==
== Backwards Compatibility Changes ==
== Internal API Changes ==