RFR: Add support for Mercurial

[Erik Duveblad via github.com]

The pull request has been updated with additional changes.

----------------

Added commits:
 - c25afe09:	Add "testedwith" and remove stray newline

Pull request:
https://git.openjdk.java.net/skara/pull/122

Webrevs:
 - full: https://webrevs.openjdk.java.net/skara/122/webrev.01
 - inc: https://webrevs.openjdk.java.net/skara/122/webrev.00-01

Updated full patch:
https://git.openjdk.java.net/skara/pull/122.diff

Fetch command:
git fetch https://git.openjdk.java.net/skara pull/122/head:pull/122