Fix attachments and content-type problems #1276 [Jamis Buck] Fix to only perform the charset conversion if a 'from' and a 'to' charset are given (make no assumptions about what the charset was) #1276 [Jamis Buck]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@1300 5ecf4fe2-1ee6-0310-87b1-e25e094e27de