Allows gnuplot to compile on OS X 10.3
There were two modifications
1. S_OUTPUT had to be renamed (conflicted with an
OpenTransport constant) In this patch, I renamed it to
S_OUTPUT_. Might want to look into putting this into some
kind of namespace to "properly" fix this problem.
2. removed the is_3d_plot extern from tkcanvas.trm. For
some reason this was causing a conflict with is_3d_plot
from command.h, even though they were supposed to be
the same thing. Very strange. Perhaps there's some
mysterious macro screwing around behind the scenes?