gEDA-dev: add-on dir name for pcb

[DJ Delorie]

> Should that directory be versioned (pcb version) too?
> 
> ~/.pcb/hids/alpha-unknown-netbsd2.0/{20060822,1.99t}/
> ~/.pcb/hids/sparc-sun-solaris2.9/20060822/

The hid structure has a size entry at the beginning.  Hids with the
wrong size aren't loaded, so in theory you could have both in the same
directory with different names and it would just work (aside from the
warning messages).  I'm ambivalent about it, though, if you want to
add VERSION to the concat for the host-specific directories, go ahead.

Of course, if the pcb version changes more often than the hid
interface, that would get annoying for the user.  Maybe check with and
without the version?  If the version directory exists, don't check the
unversioned one?  That way you can have "latest" for normal work, and
a versioned one for older versions you still occasionally use.

Another solution is to put it in $exec_prefix instead ;-)