gEDA: gnetlist enhancements

[mcmahill-at-NOSPAMmtl_dot_mit_dot_edu]

I have a suggestion for gnetlist which should be pretty easy to implement.
When m4 is called in gnet-PCBboard.scm 
I would suggest adding the current directory as well as $HOME/.pcb/ and
something like ${datadir}/pcb/ to the include path specified with -I.
I'm too much of a guile novice to know how to access $HOME.  The
${datadir}/pcb part I guess would be done via autoconf.

Then in the common.m4 file which is part of PCB, at the end, add the
lines:

sinclude(site-config.inc)
sinclude(user-config.inc)
sinclude(proj-config.inc)

The sinclude() function will include the file if it exists and do nothing
if it does not exist.  This way, a site admin can add
${datadir}/pcb/site-config.inc to provide new footprints on a site-wide
basis (without additional modifications to a file which installs as part
of PCB), a user can have their own libraries that they always use by
making a $HOME/.pcb/user-config.inc file and they can have per-project
footprints by putting a proj-config.inc file in their project directory.


The other change which would be very useful is to have an autoconf check
to find GNU m4 (instead of a system m4 which may not be GNU m4) and then
appropriately substitute that into gnet-PCBboard.scm.


I think these 2 changes would really help with making the PCB interface
work nicer and easier.

-Dan