More regexp corrections and tweaks

More regexp corrections and tweaks

From suggestions by Mattias Engdegård in:
https://lists.gnu.org/r/emacs-devel/2019-03/msg00131.html
* lisp/arc-mode.el (archive-rar-summarize):
* lisp/gnus/gnus-art.el (gnus-button-valid-localpart-regexp):
* lisp/language/ethio-util.el (ethio-fidel-to-tex-buffer):
* lisp/nxml/rng-uri.el (rng-file-name-uri):
* lisp/org/org-mobile.el (org-mobile-apply):
* lisp/progmodes/cperl-mode.el (cperl-init-faces):
* lisp/progmodes/fortran.el (fortran-fill):
* lisp/progmodes/mantemp.el (mantemp-remove-comments)
(mantemp-remove-memfuncs, mantemp-insert-cxx-syntax):
* lisp/speedbar.el (speedbar-directory-buttons-follow):
* lisp/vc/add-log.el (change-log-font-lock-keywords):
Fix more regular expressions that seem to be typos or infelicities.