Please write image files in a vector graphics format, when possible, and
generate the .png and .pdf versions on the fly (see ../Makefile).  

Currently supported tools are dia and tgif.  xfig could be added similarly
if someone wants to add it.  The main requirement for adding another format
is that the tool to edit it is freely available and that a cron script can 
autogenerate the pdf and png from the figure source.

Store the .dia, or .obj versions in mercurial, but not the .png or .pdfs.  
If the figure is not available in a vector graphics format, store both
a .png and a .pdf version in this directory.

If you add a source (.dia, .obj) file here, remember to add it to
the list of figure sources in the Makefile in the directory above

Note:  tgif can convert from .obj to .pdf, but the pdf that results takes
up a whole page.  Instead, we convert to an intermediate .eps step, and
then run epstopdf.
