add ancestry/age-based BuildChooser branch filter

[kostmo]

Selects branches to build based on commits contained in their ancestry.

This is useful for introducing new Jenkins jobs that are specific to some new feature in the repo, without causing retroactive builds of (potentially thousands of) branches that do not support that feature.

[buildhive]

Jenkins » git-plugin #391 FAILURE
Looks like there's a problem with this pull request
(what's this?)

[ndeloof]

I'd prefer this to be implemented as an extension (see recent refactoring branch, now merged into master), so that we don't get the main configuration "polluted" with hundred options as it has been with previous releases (git plugin had two nested "advanced" sections ...)

Other possible implementation option is for buildChooser to expose it's own configuration in job form, this is not the case yet. Seems a reasonable change for such use-case

[jenkinsadmin]

Thank you for a pull request! Please check this document for how the Jenkins project handles pull requests

[cloudbees-pull-request-builder]

plugins » git-plugin #128 FAILURE
Looks like there's a problem with this pull request

[cloudbees-pull-request-builder]

plugins » git-plugin #129 FAILURE
Looks like there's a problem with this pull request

[MarkEWaite]

As far as I can tell, this is now implemented and available in git plugin 2.3.1.