Bug fix
=======

Null pointer on multiple signatures
if only the first is verified.

in db_sql_dmarc_agg_record substitute
COUNT(*) with COUNT(DISTINCT(m.id))


Other changes:
==============

Skip DB if there is no db_backend.
Previously, the presence of db_statements
was enough to trigger DB functions, and
the absence of db_backend would cause an
error.  Now it should be enough to
comment out db_backend.