narrow: move changegroup.supportedoutgoingversions() override to core
Also document why we need cg3 or higher.
Differential Revision: https://phab.mercurial-scm.org/D2488
FROM fedora:20RUN yum install -y \ gcc \ gettext \ make \ python-devel \ python-docutils \ rpm-build# For creating repo meta dataRUN yum install -y createrepo