Don't crash when a new attachment is added.

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".
Fix the collision with Object#hash.

Closes #678. Closes #450.
Bump to 2.5.0
Provide content type of file to fog.
save content type of the file with fog storage engine
Can encrypt files on s3 with :s3_encrypted => true option
s3_encryption => true is now s3_server_side_encryption => :aes256
Hide ActiveRecord-specific stuff in the Railtie
allow proc for fog_directory so its possible to call model methods to set the directory
allow proc for fog_host
allow proc for fog_credentials
Bump to 2.5.1
changed is_a?(Proc) to responds_to?(:call) for better flexibility
The Gemfile.lock was updated, too.
Update Travis configuration to use new alias

Travis CI deprecated and remove the rbx-2.0 alias after rbx project
merged stuff back to master branch.
Remove .gitignore from test directory
Merge pull request #711 from maxigs/dynamic-fog-configuration

Simple addition to allow procs in the fog_config_options (bucket-name, authentication, and host)
Some style change
Remove the questionmark filename test for real file
Replacing all special characters to underscore

Fixes #703