Major changes from v429:
* Don't pass "-" to non-pipe LESSOPEN unless it starts with "-".
* Allow a fraction as the argument to the -# (--shift) option.
* Fix highlight bug when underlined/overstruck text matches at end of line.
* Fix non-regex searches with ctrl-R.
Approved by: re (kensmith, kib)
similar to the zmore script that comes with gzip (and in fact, in most
Linux distros, zless is a symlink to that very same zmore script) but has
the advantage that you get the correct file name on the less status line,
and can use :n and :p to navigate back and forth between multiple files.
MFC after: 1 week
