[changeset] improved support for pdf output

[Michael D. Godfrey]

> The bounding boxes should be very different, but the plots should be 
> the same. 
I agree: that is the target for eps vs. ps.  But, I think that pdf 
should in effect be a
converted pdf.  pdf is commonly used for inclusion in documents, so a 
"tight"
bounding box is important.
> I have a changeset prepared that renders the correct fontsize across 
> all terminals, but there are still some "features" of gnuplot that it 
> *may* be breaking (the text is not positioned correctly for bitmaps).
Sounds good.  If you can deal with the bounding box for pdf, it should 
be done.

If anyone else thinks differently about the bounding box for pdf now 
would be a good
time to say so.  I will recheck Matlab, but I think it has a "tight" BB 
for pdf.

Michael