releasenotes: don't abort is there is a bad formatted entry for releasenotes While producing releasenotes for (4.3::), releasenotes aborts with error because of some bad formatting of releasenotes in some commits. Instead of aborting, this adds warning message which will help us in skipping them and telling user about it. Differential Revision: https://phab.mercurial-scm.org/D1097