Various small changes in addition to:

Various small changes in addition to:
(Killing Emacs): Expand and clarify description of
`kill-emacs-query-functions' and `kill-emacs-hook'.
(System Environment): Expand and clarify description of `getenv' and `setenv'.
(Timers): Clarify description of `run-at-time'.
(Translating Input): Correct description of `extra-keyboard-modifiers'.
(Flow Control): Correct description of `enable-flow-control'.