templatekw: make {file_*} compare to both merge parents (issue4292)

Authored by martinvonz.


templatekw: make {file_*} compare to both merge parents (issue4292)

This redefines the {file_adds}, {file_dels}, {file_mods} template
keywords by getting the lists from the recently introduced context
methods instead of getting them from status compared to p1. As
mentioned before, these are better defined on merge commits. The total
number of files from the three lists now always add up to the number
of files in {files}.

I timed this command:

hg log -r 4.0::5.0 -T '{rev}\n {file_mods}\n {file_adds}\n {file_dels}\n'

It went from 7.6s to 5.6s with this patch. So it's actually faster
than before.

Note that the "files:" field in the bazaar test log output was using
"{file_mods}" (not "{files}" as one might think based on the label).

Differential Revision: https://phab.mercurial-scm.org/D6369