narrow: don't compress the bundle2 when sending 'error:abort'
This is similar to waht getbundle() does and also explicitly specifies that we
should get a compressed bundle2 in normal cases when not sending 'error:abort'.
Differential Revision: https://phab.mercurial-scm.org/D4934
#require docutils gettext
$ $TESTDIR/check-gendoc ru
checking for parse errors