Fix some Texinfo markup

Fix some Texinfo markup

* doc/misc/gnus-faq.texi (FAQ 3-11):
* doc/emacs/frames.texi (Tab Bars): Consistently use @var with
lower-case metasyntactic variables and @minus instead of a dash.
(Text-Only Mouse):
* doc/emacs/files.texi (Auto Revert):
* doc/emacs/misc.texi (emacsclient Options)
(Embedded WebKit Widgets):
* doc/lispref/control.texi (pcase Macro):
* doc/lispref/debugging.texi (Backtraces):
* doc/lispref/files.texi (Truenames):
* doc/lispref/frames.texi (Management Parameters):
* doc/lispref/os.texi (Time Calculations):
* doc/lispref/text.texi (Parsing JSON):
* doc/misc/efaq-w32.texi (Other versions of Emacs, Debugging)
(Swap Caps NT, Printing, Bash, Developing with Emacs):
* doc/misc/efaq.texi (New in Emacs 25):
* doc/misc/emacs-gnutls.texi (Help For Users):
* doc/misc/message.texi (Using S/MIME, Passphrase caching):
* test/manual/etags/tex-src/gzip.texi (Overview): Use @. when a
sentence in the middle of a paragraph ends with an upper-case letter
as per "(texinfo) Ending a Sentence".