Compatibility issue with new mercurial plugin

The latest jenkins mercurial plugin supports tags and now stores the
branch name in a '//revision' element rather than the '//branch'
element.
Allow ignoring old mercurial branches

autojobs will not consider branches that are older than the specified
age. This can be configured using the 'maxbranchage' setting in the yaml
file (age in days). This feature can be deactivated if the maxbranchage
is set to 0. It has a default value of 0 (deactivated).