gEDA-dev: add-on dir name for pcb

[Igor2]

On Sun, 1 Oct 2006, DJ Delorie wrote:

>
>> - Wouldn't it be better to have a config file (a list of file names) to
>> load instead of loading all hids found in specific dirs? That would allow
>> the user to load hids from non-default directories or to turn off loading
>> hids without renaming or deleting the lib files.
>
>That makes it difficult to install hids through, say, an rpm, because
>it would need to modify an existing file.  Many of linux's configury
>works this way; by adding file fragments to a .d directory rather than
>modifying a shared config file; installing all available hids in a
>directory is a similar practice.

Ok, what about a mixed approach: first check the config file, if it does
not exist, fall back to "load all". This way distros with package managers
unable to deal with such config files would just go without config
files. I guess once the user decides to write a config file by hand, we
can assume he will keep on updating it. 

>> - Where do hid-specific data files go? I mean if a hid uses data files for
>> some reason, we should name default dir for them as well.
>
>That's mostly up to the hid; we can provide some global variable that
>reflects $prefix if it wants to use that, or the hid can create an
>attribute for the user to specify directly.

The global variable idea seems to be good for this.