Merge from origin/emacs-26

Merge from origin/emacs-26

e133b63 (origin/emacs-26) Avoid adverse side effects of fixing bug#21824
cc8f334 Document changes called out in NEWS
20ecc52 ; * etc/NEWS: Document recent change in 'thing-at-point'.
1fc5283 ; INSTALL: Fix a typo in the last commit.
24f240d Tiny doc updates re yum/dnf etc
41c2d25 Remove unused variable
1e3b3fa Fix (thing-at-point 'list) regression (Bug#31772)
219893a Clarify meaning of '*'
41cdda2 * etc/PROBLEMS: Document Ubuntu 16.04 issue.
1c22f03 Increase default value for imenu-auto-rescan-maxout
ee84389 Improve recent change to ELisp manual
ff374e4 * doc/lispref/display.texi (SVG Images): Improve wording.
3a0caf6 * doc/lispref/display.texi (SVG Images): Fix a typo.  (Bug#32...

Conflicts:
	doc/lispref/lists.texi
	etc/NEWS