More proofreading of the Emacs manual

More proofreading of the Emacs manual

* doc/emacs/trouble.texi (DEL Does Not Delete): Improve wording.
(Screen Garbled): Mention the command name.
(Bug Criteria): Mention that problems in packages should first be
reported to the respective maintainers.
(Checklist): Fix wording.
(Contributing, Copyright Assignment): Minor copyedits.
* doc/emacs/misc.texi (Amusements): Remove Landmark.
* doc/emacs/picture-xtra.texi (Tabs in Picture): Improve wording.
(Rectangles in Picture): Add a cross-reference to "Registers".
* doc/emacs/misc.texi (Gnus Group Buffer, Gnus Summary Buffer):
Mention command names in parentheses.
(Gnus Summary Buffer): Document "M-r".
(Network Security): Document that current NSM works with TLS
encryption.  Fix markup.
(Document View): Improve wording and fix a typo.
(DocView Conversion): Rephrase description of
doc-view-cache-directory.
(Single Shell): Mention variables that control when shell output
appears in the echo area.
(Shell Mode): Improve wording.
(Shell Prompts): Fix a typo.
(Shell Ring, Term Mode): Mention command names.
(History References): Add a cross-reference to "Rebinding".
(Remote Host): Mention SSH.
(TCP Emacs server): Improve wording.
(emacsclient Options): Minor improvements.
(PostScript): Fix wording.
(PostScript Variables): Mention that ps-font-size could be a cons.
(Sorting): Minor improvements.  Suggested by Michael Albinus
<michael.albinus@gmx.de> in emacs-manual-bugs@gnu.org