custom_variable_classes module names

Hi,

While preparing a module which should make its way to pgfoundry CVS soon
(BSD licenced), I stumbled accross a naming problem when using
custom_variable_classes.

It'll actively refuse the name if it contains an underscore (_):
ERROR: unrecognized configuration parameter "pre_prepare.relation"

I've resigned to be using the name preprepare.relation, but maybe you'd
agree with me that's a bug (documentation doesn't refer to this
limitation, but I wouldn't consider this a doc related bug).

Regards,
--
dim