Merge from emacs-26

Merge from emacs-26

e62ad04963 Fix sgml-mode handling of quotes within parens (Bug#36347)
06b35b2f92 ; * lisp/frame.el: Enhance add-variable-watcher commentary.
572e34bb6f Rename 'make-symbolic-link' argument NEWNAME to LINKNAME
04477adedc Check that length of data returned by sysctl is non-zero
81535eeadb * test/lisp/progmodes/python-tests.el (python-virt-bin): D...
9d48979ca8 Fix Python tests depending on system-type
fcf6cc3177 Fix problem with wdired test when symlinks cannot be created.
4701e0663e Improve wording of documentation of click events

# Conflicts:
#	lisp/textmodes/sgml-mode.el
#	test/lisp/textmodes/sgml-mode-tests.el