Merge from origin/emacs-25

Merge from origin/emacs-25

d4c6774 Fix missing point information in undo
3a9d629 Avoid crashes when buffer modification hooks clobber match data
178b2f5 Note combine-and-quote-strings doesn't shell quote
dec7567 Explain when package-initialize isn't called
113d1e2 Fix escaping in sh-indent-after-continuation docstr
80e2044 ; * etc/NEWS: Improve previous change.
5bb9e6c ; * etc/NEWS: Document how to avoid horizontal scroll bars.
38f4b8e Clarify the documentation of back-references in replacements