Form cache typos

[hhamon]

Some minor typos in cache and forms chapters

[weaverryan]

Data is always plural, but using it correctly still sounds really strange in English. It might be best to avoid it in this way - I've modified the language slightly. Also, isn't it better to say that we're validating the object and not the data?

One question - we say "If a POST request...", but there's no actual if statement in the action. Should the wording be written as if it only handles the form submit or should there be an if statement added? Put better, which pattern should we be teaching the reader?

Thanks