gsch2pcb should use PCB Import action

[Peter TB Brett]

 affects: geda
 tag: gsch2pcb
 done

gsch2pcb has a number of problems at the moment:

1) Because it doesn't properly check that footprint names are safe for
   m4 before running m4, it suffers from problems with some special
   characters (particularly '-') in footprint names (bug 698806).

2) Hard-coded (at compile time) paths for PCB mean that it can't find
   footprints installed with PCB if PCB is installed to a different
   prefix to that which gsch2pcb was expecting (bug 698582).

A way around this would be to re-implement gsch2pcb to use PCB directly
to do the import, by feeding PCB a set of actions on standard input
along with some carefully-crafted command-line options. In particular,
the recently-added Import option, might be useful:

  http://pcb.gpleda.org/pcb-cvs/pcb.html#import-Action

The main issue would be working out how to emulate all of the existing
functionality of gsch2pcb through PCB, and would be likely to require
cooperation from the PCB development team.