Initializer the remote_handlers in init so they can be appened to later.

Make retrieve_remote support other methods besides GET (so it can
do HEAD).
Merge branch 'master' of github.com:cdent/tiddlywebplugins.remotebag
Merge branch 'master' of github.com:cdent/tiddlywebplugins.remotebag

Conflicts:
	tiddlywebplugins/remotebag.py