Fix feed-detail.php tagging.

The tag field has been isolated into its own form, and now responds to key events properly.  The feed-detail.php page will no longer unexpectedly reload instead of submitting a request to add a new tag with a carriage-return.
Use prototype.js framework for feed-detail.php actions.

Replaced inline js with scripted observe() hooks, for tag-setting interactions.

Also try to handle form submissions.
Retain and report the most recent status of a feed update.

If a feed fails to update, the reason will be stored in the newly-added column 'feed_cache_last_attempt_status' in FOF_FEED_TABLE.  The new function fof_db_update_attempt_status() will set and clear the value.

Fixed some of the SimplePie error-checking to use the public error method rather than the internal error property.

Irregular statuses are now indicated in the sidebar feed icon slot, as well as on the feed detail page.
Fixed MySQL db migrations.

MySQL still doesn't like single quotes.  Table migrations should work now.