RFR: Make ext.py compatible with hg5 api

[Jorn Vernee via github.com]

The pull request has been updated with additional changes.

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

Added commits:
 - 91fb200e:	Switched to using `version()` instead of `versiontuple()`, since the former is supported by older versions

Pull request:
https://git.openjdk.java.net/skara/pull/67

Webrevs:
 - full: https://webrevs.openjdk.java.net/skara/67/webrev.01
 - inc: https://webrevs.openjdk.java.net/skara/67/webrev.00-01

Updated full patch:
https://git.openjdk.java.net/skara/pull/67.diff

Fetch command:
git fetch https://git.openjdk.java.net/skara pull/67/head:pull/67