Print using pipes

[Ben Abbott]

I've pushed the changeset to print using pipes.

        http://hg.savannah.gnu.org/hgweb/octave/rev/064aaf82222f

For the gnuplot backend a file is written by gnuplot (not using pipes). If it 
is necessary to convert of modify the file a system command with pipes is used.

For the FLTK backend, the GL2PS output is piped directly.

Help testing is needed to ensure everything works for all platforms.

Some notes on functionality.

(1) Support for a tight bbox and eps preview is included.
(2) To produce a tight bbox and preview, for eps files, epstool is used. 
(3) -tight & -preview do not work at the same time (epstool limitation).
(4) To produce the proper papersize and paperposition, ps and pdf
    output are always derived from eps using gs.
(5) Specifying the fontname and/or size using -FFONTNAME:SIZE
    works for all formats.
(6) Specifying the canvas size as -SXSIZE,YSIZE works for all formats.
    Depending upon the format the size is interpreted as points or as
    pixels.
(7) epslatexstandalone is not presently working for GL2PS output.
(8) The piping implementation for GL2PS output needs testing.

Short description of the implementation.

__print_parse_opts__.m
  * parses the input and sets defaults.
  * checks for gs, epstool, fig2dev, lpr, & pstoedit in EXEC_PATH.

print.m
  * Temporarily modifies figure properties to match the print options.
  * Contains the auxillary funcitons: epstool, fig2dev, lpr, pstoedit,
    and shell_translation.
  * Passes handles to auxillary functions, used to convert formats,
    to __fltk_print__ and __gnuplot_print__.

__fltk_print__.m
  * Produces output via pipes.
  * All output is derived from eps.
  * Relies on epstool, fig2dev, gs, lpr, and pstoedit.

__gnuplot_print__.m
  * Used gnuplot to produce an output file.
  * Many (most?) native gnuplot formats are supported.
  * Conversion to most other formats is handled by a system call.
    The system call may include pipes.
  * Relies on epstool, lpr, and gs.
  * Currently does not use fig2dev, or pstoedit.

Ben