obslog: add display of precursor information to the default template
This will still only be output when the user passes --precursors to the command
(otherwise the data just won't be there).
This addresses a common user request, where they actually would find more
intuitive to use --precursors --no-successors.
#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