fixes #588 . Attempt to log warning message when 2 models use same attachment name with default url interpolation

There was an issue on assignment another S3 attachment object to another object whereas calling #to_file on S3 attachment will create a Tempfile, which would then having a different file name than original version.

By caching the filename first before calling #to_file, we're ensuring that filename is the original one.

Fixes #9

Thank you @Bonias for reporting in

Closes #590

This will make sure Interpolations is comply with Ruby's Object#hash

Closes #569, Closes #603

This test will generate a basic Rails application, include Paperclip
into Gemfile, and call basic `has_attached_file` in the model. This will
make sure that we're not messing up any of the configuration and
integration for our gem and the Rails framework.

Thanks @GMFlash!

Closes #586

Thank you @excid3 for suggestion.

Closes #582

We've ignored the lock file at 3f56e703, so we should remove it as well.

However, this will make sure that you can always change it to something else afterward.

There's currently no test for this, but after I've tried this with the `integration_test` branch, I can confirm that logs are written to `log/test.log` as it should.

Closes #581

Thank you @eric-hu for reporting this regression.

Closes #583

Conflicts:
	README.md

Fixing destroy callback to delete files just when model destroy method was completed successfully (i.e. no exception like 'foreign key constraint violations' was raised)