Change column types of spamfilter_policy

Change column types of spamfilter_policy for compatibility with latest perl versions.

ALTER TABLE spamfilter_policy CHANGE spam_tag_level spam_tag_level DECIMAL(5,2) NULL DEFAULT NULL, CHANGE spam_tag2_level spam_tag2_level DECIMAL(5,2) NULL DEFAULT NULL, CHANGE spam_kill_level spam_kill_level DECIMAL(5,2) NULL DEFAULT NULL, CHANGE spam_dsn_cutoff_level spam_dsn_cutoff_level DECIMAL(5,2) NULL DEFAULT NULL, CHANGE spam_quarantine_cutoff_level spam_quarantine_cutoff_level DECIMAL(5,2) NULL DEFAULT NULL;