Add keyword `figname' to pic, specifying the name of the picture

Add keyword `figname' to pic, specifying the name of the picture
box in TeX mode.  Based on a patch from William J Poser
<wjposer@unagi.cis.upenn.edu>.

* src/preproc/pic/pic.y: New token `FIGNAME'.
(macro_name): New rule of type <str>.
(placeless_element): Handle `FIGNAME'.
* src/preproc/pic/lex.cpp (lookup_keyword): Add `figname'.
* src/preproc/pic/main.cpp (graphname): New global variable.
(do_picture): Initialize `graphname'.
* src/preproc/pic/pic.h: Updated.
* src/preproc/pic/tex.cpp (tex_output::start_picture): Use
`graphname'.
Simplify TeX code.
(tex_output::text): Beautify output.
* src/preproc/pic/object.cpp (object_spec::~object_spec): Deallocate
`shaded' and `outlined' unconditionally.
* NEWS, src/preproc/pic/pic.man, doc/pic.ms: Updated.
Minor improvements.

* PROBLEMS, README.CVS: Mention that bison version 1.875b or
greater is necessary.