cmdutil: changeset_printer: use methods of filectx/changectx.
This allows extensions that modify changeset metadata (e.g.
description) by overriding methods of changectx to get consistent
behavior from all log-like commands, regardless of whether templates
or styles are used. Without this, overriding changectx methods works
if you use styles or templates, but not with default log format.
This meant adding filectx.extra() for consistency with changectx.
#!/bin/sh
hg init repo
cd repo
echo foo > foo
hg ci -qAm 'add foo'
echo >> foo
hg ci -m 'change foo'
hg up -qC 0
echo bar > bar
hg ci -qAm 'add bar'
hg log
cd ..
hg init copy
cd copy
echo '% pull a missing revision'
hg pull -qr missing ../repo
echo '% pull -r 0'
hg pull -qr 0 ../repo
hg log
echo '% pull -r 1'
hg pull -qr 1 ../repo
hg log
# this used to abort: received changelog group is empty
echo '% pull -r 1 again'
hg pull -qr 1 ../repo