convert: make contents of "extra" dict available from sources, for sinks. This breaks hash preservation for hg->hg conversion, as each converted change gets a convert_revision item added to its extra dict. Ugh.

import doctest

import mercurial.changelog
# test doctest from changelog

doctest.testmod(mercurial.changelog)

import mercurial.httprepo
doctest.testmod(mercurial.httprepo)