Back-config attribute names

[Hallvard B Furuseth <h.b.furuseth@usit.uio.no>]

Backends can have options with the same name but very different
semantics, and so far this seems to be reflected in back-config
attribute names.  That could get messy, in particular with contrib or
private backend modules written using some other backend as a template.

I think a config parameter's attribute name in general should be
something like 'olc(Db?)<backend>-<parameter>', unless the parameter is
expected to be used the same way in all backends that use it.
No hyphens in backend names.

Overlays use 'olc<overlay><parameter>'.  Backends could do the same if
we are never supposed to have an overlay and a backend with the same
name...  However, note that we could still get name conflicts if the
name of one overlay is the beginning of the name of another overlay.
'olc<overlay>-<parameter>' would be better.

Existing config parameters could keep their current names as secondary
names, but get new names as the first name.

-- 
Hallvard