auto-generate index for documentation

[Ethan M. <merritt@u.washington.edu>]

I've uploaded a patch to SourceForge (#1192870) that modifies
the generation of gnuplot.tex from .../docs/Makefile.
It uses the makeindex utility to create an index, which then
propagates into the TeX-derived documenation (dvi, PostScript, pdf).

Please report any problems.
For instance, is makeindex universally distributed with TeX?

Also please suggest procedures for identifying what keywords
in the documentation are worth adding to the index.  Right now
it's fully automated, but doesn't catch everything it should.

-- 
Ethan A Merritt
Biomolecular Structure Center
University of Washington 98195-7742