Fixed that records fetched with piggy-back attributes or through rich has_and_belongs_to_many associations couldn't be saved due to the extra attributes not part of the table #522 [Eric Anderson]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@483 5ecf4fe2-1ee6-0310-87b1-e25e094e27de