Per #9999 revert blank? to empty?

This is both faster and more correct, added tests to make sure this is not reverted again.

We don't actually need a rails.png in the AP fixtures, the tests
that use it don't actually try to load the file.

We also don't need to get rid of it with the dummy reset either.

Finally, it's not needed in the sample application that's included
with the Rails Guides.

Since it's not a real file any longer, no need to worry about
removing it when we reset the dummy.

Mentioned in a comment in e90c2d02 by @frodsan.

Rename DummyKeyGenerator -> LegacyKeyGenerator

Cookies refactoring

Fix permanent cookie jar accessor typo

I'm giving @jlsuttles credit on this commit because she gave me the idea
and the actual converted image in 952289aa.

Remove rails.png.

No reason to have a file, we've got data-URIs now! It didn't make sense
to me that you no longer have to remove public/index.html, but you still
need to remove rails.png. This means that you won't have to any more
when making a new Rails app.

Prefer find_by over dynamic finders in rdoc

each_with_index  => each as we dont use index

Changed the guides for associations, warning about race conditions when checking for distinctness

commit a1bb6c8b which changes the naming). I've also provided an
example of how distinctness when inserting into an association can be
achieved.

Turning on warnings in "rake test" for railties

Unserializing YAML attributes can silently fail in development mode

Extract Firebird / Sqlserver / Oracle database tasks, and They should be deprecated.

write sql queries to terminal

no need to invoke to_s before applying intern