Added validate_doc_update from toolbox.

I stripped all of the stupid design restrictions but left the 'read-only for
guests'-feature. My database-server is public only a couple of hours each
workday except Friday, so it seems very very very unlikely that sensitive data
is hi-jacked.
Improved validate_doc_update to avoid identical revisions.

JSON.stringify is probably not the best tool for this, but I very much enjoy
the prospect of a clean document revision history from now on!!
Modified upload.html to respect _bulk_docs response.

Documents with errors are skipped but the stored _rev still applies and is
copied to feature.rev. Not sure that the script will go without uncaught
exceptions if for instance the user is logged out.
Reviewed some comments and error messages.

The latter should be sentences instead of exclamations, I suppose.