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 a
cd a
touch empty1
hg add empty1
hg commit -m 'add empty1' -d '1000000 0'

touch empty2
hg add empty2
hg commit -m 'add empty2' -d '1000000 0'

hg up -C 0
touch empty3
hg add empty3
hg commit -m 'add empty3' -d '1000000 0'

hg heads

hg merge 1
# before changeset 05257fd28591, we didn't notice the
# empty file that came from rev 1.
hg status
hg commit -m merge -d '1000000 0'
hg manifest --debug tip