attempt to upgrade acts_as_taggable_on

Getting strange ArgumentError: wrong number of arguments (0 for 1)
when running
test_tagged_with(TaggingTest)
rewrite scopes using 3.1 syntax
castle_gates: do not require holders to be an association

User.peers now is a method that returns a simple relation.
This broke the castle_gates handling of the holder.

However we do not need the Holder to be a proxy proxy.
We can simply represent it with the owner record and a symbol.
ensure parent_id is still present when clearing council permissions
fixture_path has to be a string
use errors.[] instead of errors.on
user association target check instead of @instance_var

The latter seems to be gone with rails 3.1 now