Filters not implemented

[harlowja]

DescribeInstances supports filters but openstack EC2 versions don't acknowledge or deny those filters (its just ignored).

When a version of EC2 is requested that doesn't support filters is passed, it should error out, instead of just ignoring them? And when a version is passed that does support them they should at least be validated...

Ie:

Filters are not valid in versions < 2010-08-31, but openstack does not reject filters or acknowledge them (beyond inherit filter for instance id) even if a version >= 2010-08-31 is provided (ie no advanced filter support)