RFR: Add Repository::abortMerge

[Erik Duveblad via github.com]

The pull request has been updated with additional changes.

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

Added commits:
 - 336ea779:	Only remove .orig files in HgRepository::abortMerge

Pull request:
https://git.openjdk.java.net/skara/pull/101

Webrevs:
 - full: https://webrevs.openjdk.java.net/skara/101/webrev.01
 - inc: https://webrevs.openjdk.java.net/skara/101/webrev.00-01

Updated full patch:
https://git.openjdk.java.net/skara/pull/101.diff

Fetch command:
git fetch https://git.openjdk.java.net/skara pull/101/head:pull/101