I have a machine with no builtin db1.85, on which I want to run postfix
(using db4) and webalizer, which can only use db1 or db2. Since db2 and
db4 do not conflict, this should be possible.

However, bdb.buildlink3.mk does not deal with this.

A very simple possible solution would be to allow specifying pkg specific
values for the default:

  BDB_DEFAULT.webalizer = db2

This, maybe accompanied by a slightly more helpful message when the default
db version is not in BDB_ACCEPTED, would allow the user to work around
the problem (i.e. manually resolve the conflichts).

What do you think?

Martin