graphics/gnuplot-5.0.0 candidate

[Makoto Fujiwara <makoto%ki.nu@localhost>]

I've imported wip/gnuplot for 5.0.0 candidate.
Please take a look, modify (if you have wip account)
or give me comments.

Existing graphics/gnuplot 4.6.6 has gnuplot.pdf in
PLIST. To get that file, I've added two targets
in pkgsrc Makefile. (That is the major change and
I'm not confident on that, that's why wip version)

Thanks a lot,
---
mef%NetBSD.org@localhost
Makoto Fujiwara, 
Chiba, Japan, Narita Airport and Disneyland prefecture.