more status_hilite threshold handling

more status_hilite threshold handling

Negative AC needed one extra change to support >-N since there was
a place in the code that assumed 0 was the lowest possible value.
(My earlier testing was with <-N which didn't have that issue.)

Make '/<N/' work as 'val < N' instead of 'val <= N', and />N/ work
as 'val > N' instead of >=.  The <= and >= behavior might have been
intentional but the only support for that I could find was that
the 'O' menu used "N or less" for '<' and "N or more" for '>' when
setting up 'absolute' rules.  If we actually want <= and >= (and we
probably do...), we should add them as more relationship operators
instead of misusing < and >.

Simplify the is_ltgt_percentnumber() case when parsing options
since input has been fully validated by the point that that test
passes.  Among other things, /<-0/ and />-0' are now accepted (as
synonums for 0; -0 doesn't mean anything special) instead of being
silently rejected and then discarding the rest of the config file.
(That bad behavior is a separate issue not dealt with here.)