Introducing `:restricted_characters` in Paperclip::Attachment.default_options  so people can override their blacklist characters by override that setting.

Fixes #703

Closes #678. Closes #450.

If a model has an existing attachment and styles, and later a new attachment is added (not just new styles), "rake paperclip:refresh:missing_styles" would crash with "TypeError: can't convert nil into Array".

#fingerprint now consistently returns nil before and after saving an attachment if the value can't be written to the db.

From https://github.com/pcreux/paperclip/commit/52374958ef83f1641cf008aead27c23b25fb842d

Conflicts:

	lib/paperclip/attachment.rb

This fixes #660

Standardize strip with resy of application.  Without to_s, causes errors like "undefined method `strip' for image/bmp:MIME::Type".

In some case, we seriously don't want to prepend the timestamp with & if there wasn't a query string there. If the original URL doesn't have any query string, we should add the ?.

The original commit came from @amazonwebservices and @trevorrowe in #579.
I had to revise the commit and make sure all the test cases are passing.
All credits still goes to those guys, thanks a lot!

    This can be used in migrations, i.e.

      create_table :users do |t|
        t.has_attached_file :avatar
      end

(three commits squashed into one by Alexey Mahotkin <squadette@gmail.com>)