Fall back to asciidoc6 html backend if html4 doesn't work. This reenables building documentation on Debian sarge, which broke after 9346a7fb3fe2.

#!/bin/sh

hg
hg -q
hg help
hg -q help
hg add -h
hg add --skjdfks
hg help diff
hg help status
hg -q help status
hg help foo
hg skjdfks

exit 0