Attention,
The Session class DB driver has undergone a structural change to the session table. The column 'ip_address' has been dropped, and replaced by a new column 'ip_hash', defined CHAR(32).
This is done because of an extra cookie hijacking protection feature, and in preparation for IPv6 support.
For those using the 'develop' branch in combination with DB sessions, your application is now broken and you'll have to change the table structure.
For those using 'master', you'll have to make this change as soon as 'develop' is merged.
For users of other branches there is no issue as this fix will not be backported. You will have to make the change once you switch though, for example when upgrading from RC3 to a newer version.