has_many association_condition

I’ve added a new option to has_many association: association_condition allowing default “primary_key = foreign_key” condition to be overridden to something more complex like “primary_key LIKE foreign_key” or “SQL_FUNCTION(primary_key, foreign_key)”

I’ve opened a lighthouse ticket and attached a diff to it. http://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/2282-has_many-association_condition-option

I’d love to get some feedback as this is my first non bug fix contribution.