Have the configuration options 'no-err' and 'no-async' work again

In an earlier attempt to simplify the processing of disabled options,
'no-err' and 'no-async' stopped working properly.  'err' and 'async'
are directories under 'crypto/', but they are special insofar that
they can't be simply skipped, like all the algorithm directories can,
so they need special treatment among the disablable things.

Reviewed-by: Tim Hudson <tjh@openssl.org>