revises implementation and documentation of csrf_meta_tags, and aliases csrf_meta_tag to it for backwards compatibilty

[#5610 state:committed]
Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

Signed-off-by: NMikel Lindsaar <raasdnil@gmail.com>

added a test for relation which checks intersection between a relation and an array works in both directions
Signed-off-by: NMikel Lindsaar <raasdnil@gmail.com>

Cheaper attribute reads and respond_to?. Add underscore-prefixed method aliased to the attribute name so it can be overridden but still called internally.

if operation is count then column_name will never be blank