Log Message:
add PKG_SYSCONFDIR/pcb, $HOME/.pcb and . to the search path for PCB m4
files.  In addition sinclude the files 'site-config.inc',
'user-config.inc', and 'proj-config.inc' to allow for per-site, per-user,
and per-project configuration instead of only per-site configuration.
This is essential for use by non-sysadmin users and users who need to
keep project specific setups.