This is the IcedTea variant of the Mercurial Forest Extension.
http://mercurial.selenic.com/wiki/ForestExtension

The original forest extension was at http://hg.akoha.org/hgforest
but is no longer maintained. Mercurial adopted the somehwat similar
concept of subrepositories as officially supported extension.
http://mercurial.selenic.com/wiki/Subrepository
This is not compatible with forests though (forsts require some
protocol extensions not supported by plain Mercurial).

This repository is maintained to support the IcedTea and OpenJDK
hackers who are still using mercurial forests. It incorporates
changes from the following two forks:
https://bitbucket.org/pmezard/hgforest-crew
https://bitbucket.org/gxti/hgforest