tidying the etc/ directory

[Glenn Morris]

I think the etc/ directory is a bit of a mess, and I'd like to propose
the following reorganization (together with the associated code
changes, which are very minor):


1. mkdir tutorials
mv TUTORIAL* tutorials/

Edit startup.el and tutorial.el.


2. mkdir refcards
mv *.ps *.eps *.tex refcards/  # except ps-prin*.ps

Either change or move most of etc/Makefile.
Change refs in man/faq.texi.


3. mv *.pbm *.xpm images/

Tiny change in src/image.c, change READMEs.


4. mv tree-widget images/

No code changes AFAICS, since tree-widget.el already looks here too.