unified FLTK & Gnuplot printing

[Ben Abbott]

I've prepared a changeset to unify the printing for both the FLTK and Gnuplot 
backends.

For both backends, ghostscript is relied upon more heavily than before. 
Ghostscript is used to produce most output formats from an eps image of the 
figure.  The output formats based upon an eps image are bmp, jpg, pbm, pcx, 
pdf, pgm, pgn, pnm, ppm, ps, and tiff. Using an eps image as the basis for most 
output formats allow all those formats to benefit from efforts invested in eps 
output.

Some improvements to Gnuplot printing include;

(1) The "-tight" option applies to all output derived from eps files.
(2) The size option "-SXSIZE,YSIZE'" applies to all output formats which accept 
size specifications.
(3) The font option "-FFONTNAME:SIZE" applies to all output formats which 
accept font specification.
(4) The "output_to_paper", "implicit_margin", and "__pixels_per_inch__" 
variables have been eliminated.
(5) As ps and pdf output are derived by placing an eps image on a page, the 
paper properties are handled precisely.

The above options also apply to the FLTK backend. In addtion, the "-mono", 
"-color", "-solid" and "-dashed" options apply to all output formats, for both 
backends, that support these line types.

Other noticeable changes are improvements in placement/spacing of the axes and 
tick labels. These improvements are most noticeable for the Gnuplot "aqua", and 
"svg" terminals. In addition, the Gnuplot "eps" output now produces the 
fontsizes specified by the object properties (before they were half the size 
... a Gnuplot feature).

While I've done a lot of testing, more is needed. In particular, I'd like to 
see printing to non-postscript printers tested on Linux, BSD, and Windows 
(mingw, cygwin, and native if possible).

If anyone has a favorite output format, please take the time to check it now 
before my feeble memory forgets the details of what I've done ;-)

If no significant problems surface by the end of the week, I'll push this 
changeset.

Ben

changeset.patch
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