progress: split up _print() method in bar-updating and debug-printing
I just thought this was clearer, but it turned out to also simplify
the next patch.
This seems to have sped up `hg perfprogress` from 1.85 s to 1.78 s.
Differential Revision: https://phab.mercurial-scm.org/D5529
#require test-repo jshint hg10
$ . "$TESTDIR/helpers-testrepo.sh"
run jshint on all tracked files ending in .js except vendored dependencies
$ cd "`dirname "$TESTDIR"`"
$ testrepohg locate 'set:**.js' \
> 2>/dev/null \
> | xargs jshint