Fix a bug when passing a method name to `:if` and `:unless` option in `validates_attachment_presence`

Fixes #631

Fix 293, 601: STI subclassing overwrites options

ones (:private and :public_read) in the s3_test
completed test for lambda permission value

formulate assert conditions

bit of work

Closes #602

So instead of having:

    http://s3.amazonaws.com/paperclip/var/www/foo.com/current/avatars/1/original/foo.jpg

because default path has the :rails_root, now you'd have:

    http://s3.amazonaws.com/paperclip/avatars/1/original/foo.jpg

This shouldn't affect your application because you'd normally set the path to some string.

Paperclip::InterpolatedString will ensure that we're not double escape the string, which was the cause of the escaped filename problem in #path method.