obslog: make changeset available to templater
obslog templating currently has very limited support for templating
the precursor changeset (when available). The only available keywords
are {node}, {rev}, and {shortdescription}. This patch makes the entire
changeset available to the templater by passing it to
formatter.context(). That function has been available since Mercurial
4.2.
#require test-repo pyflakes
Copied from Mercurial core (60ee2593a270)
$ cd "`dirname "$TESTDIR"`"
run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)
$ hg locate -I 'set:(**.py or grep("^#!.*python")) - removed()' 2>/dev/null \
> | xargs pyflakes 2>/dev/null