Berkeley DB uniquename handling

[Clint Adams]

> What does that feature change in Berkeley DB?

All symbols are compiled with the uniquename suffix.
For example, db_create becomes db_create_4000 in db4.0 compiled with
--enable-uniquename, db_create_4001 in db4.1 compiled with
--enable-uniquename, and db_create_embedded in either compiled with
--enable-uniquename=_embedded .  It's their way of symbol
versioning.

This could probably be done without manual intervention, since
db.h will contain something like

#define db_create db_create_4000

However, bogofilter's configure doesn't attempt to parse this, so the
AC_EGREP_HEADER succeeds, then the AC_CHECK_LIBS fail.