Offer to save each buffer, then kill this Emacs process.
With prefix ARG, silently save all file-visiting buffers without asking.
If there are active processes where `process-query-on-exit-flag'
returns non-nil, asks whether processes should be killed.
Runs the members of `kill-emacs-query-functions' in turn and stops
if any returns nil. If `confirm-kill-emacs' is non-nil, calls it.