debugformat: fix formatting for compression level
`bytes(<int>)` gives a very different result as `str(<int>)` and the display
of `hg debugformat` have been broken for a while as a result.
#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