(Newsgroup archives): Update URLs of GNU mail archives.

(Newsgroup archives): Update URLs of GNU mail archives.
(Reporting bugs): Suggest using `M-x report-emacs-bug'.
Add xref to `(emacs)Reporting Bugs'.
(Getting a printed manual): Add URL to other formats of the manual.
(Common requests): Fix menu.
(Highlighting a region): Remove ref to `Turning on syntax highlighting'.
(Horizontal scrolling): Mention `truncate-partial-width-windows'.
(Inserting text at the beginning of each line): Add pxref to
`Changing the included text prefix'.
(Forcing the cursor to remain in the same column): Mention `track-eol'
and `set-goal-column'.  Add pxref to `(emacs)Moving Point'.
(Replacing text across multiple files): Add keybinding `Q' for
`dired-do-query-replace'.