chgserver: discard buffered output before restoring fds (issue6207)
On Python 3, flush() appears not discarding buffered data on EPIPE, and
the buffered data will be carried over to the restored stdout.
#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