Fix for issue 5090

https://github.com/diaspora/diaspora/issues/5090

Changing error message wording and providing more information to user when status message is too long. I can add a test if you'd like, but none existed before. All tests pass. I'm not a huge fan of the controller change (@status_message.errors.messages[:text].join('. ')) as it looks clunky and the model change (adding a proc to the validates message) looks odd, but that seems to be the way to add the current message length.

I think this also will fix https://github.com/diaspora/diaspora/pull/5099 as it appears to be similar if not identical
Interesting, where did you find the messages method? Only can make out full_messages :)

What about: `format.json { render text: @statu_message.errors.full_messages_for(:text).to_sentence, status: 403 }`?