More updates to misc.texi.

More updates to misc.texi.

* doc/emacs/misc.texi (Single Shell): Don't document Lisp usage of
shell-command.  Tidy up discussion of synchronicity.  Add index
entries for async-shell-command.
(Interactive Shell): Note that M-x shell uses shell-file-name.
Note change in behavior in Emacs 24.
(Shell Mode): Shell mode now uses completion-at-point.
(Shell Prompts): Emphasize that comint-use-prompt-regexp isn't the
default method for recognizing prompts nowadays.
(Shell Ring): Add xref to Minibuffer History.
(Directory Tracking): Explain Dirtrack mode in more detail.
(Term Mode): Fix index entries.
(Paging in Term): Merge into Term Mode.
(Serial Terminal, Emacs Server, emacsclient Options): Copyedits.
(Printing): Fix xref.  State default of lpr-switches.
(PostScript): Remove obsolete sentence.  Omit description of
non-interactive behaviors.
(Hyperlinking): Improve description.
(Browse-URL): Using compose-mail for mailto URLs is the default.
Document browse-url-mailto-function.
(Goto Address mode): Add index entries.  Add xref to Browse-URL.
(FFAP): FFAP is not a minor mode.
(Amusements): M-x lm was renamed to M-x landmark.  Document
nato-region.