Merge from origin/emacs-26

Merge from origin/emacs-26

22922c7 (origin/emacs-26) * doc/emacs/entering.texi (Entering Emacs):...
59657c4 Document 'window-at-side-p' in the Elisp manual
2b35ed0 Document external-debugging-output in the Elisp Manual (Bug#2...
db6564c Fix scroll-margin docstring (Bug#13791)
732d1b9 Clarify that `ansi-term' is almost the same as `term' (Bug#18...
f706c59 Update manual description of locate-file (Bug#23650)
1602262 Clarify effect of print-gensym (Bug#27776)
53e9fa2 * lisp/custom.el (defcustom): Fix docstring (Bug#27891).
607cc4e Define cl-type-definition button type as needed (Bug#28899)
9e6889c Emphasize that GPG passphrase caching is temporary (Bug#29907)
4b5711b Fix @examples in cc-mode.info, where lines were getting glued...
71961f1 Minor change in "Mode Line" section of Emacs manual
55a2b76 More fixes in the Emacs manual