weechat-sauron Check if sauron is available. Warn otherwise.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Demote errors to messages in `weechat-notify'.

This is a workaround to fix missed notification when an error occurs
in a notification handler.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>