[PATCH] volatile-data plots now handle 'reversed' ranges during replots

[Dima K. <gn...@di...>]

I'm attaching another patch. This one adds support to the "reverse"
ranges setting for replots of volatile data. This is similar to the
previous ranging fixes, where the setting was respected for the original
plot, but ignored for replots.

I'm also including the test cases I used to validate this. For all the
test cases, I made sure that both the original plot and a replot looked
good.

Lastly, I'm really not at ease with these patches. Currently there are
separate code paths for volatile and from-a-file data; these paths get
out of sync, and issues such as this arise. I'm assuming that where
reading data from files gnuplot can (and does) take multiple passes
through the data, which is impossible when reading a pipe. Does anybody
know why multiple passes are made? Is it a major undertaking to reduce
this to a single pass, so that all data becomes "volatile" and we can
get rid of the multiple code paths?

dima