upgrade: register compression as a format variants
Compression is a promising vector for speedup, let us make it easier to check
the compression used and upgrade existing repository.
#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' \
> -X mercurial/templates/static/excanvas.js \
> 2>/dev/null \
> | xargs jshint