This refines the fix for bug#72561: commit 0a50019308 fixes
the bug by changing `ert--pp-with-indentation-and-newline`,
but it turns out that `pp` was inconsistent (it sometimes
indented the subsequent lines correctly and sometimes not,
depending on the current-buffer's major mode).
So the fix really should be in `pp`, which is what this patch does.
* lisp/emacs-lisp/pp.el (pp): Appropriately indent subsequent lines
if the first line is not inserted in column 0 (tho only when
printing into a buffer since otherwise it's somewhere between
ill-defined and impossible to implement).
* lisp/emacs-lisp/ert.el (ert--pp-with-indentation-and-newline):
Remove the indentation code after `pp` which was just working
around the bug in `pp`. Also remove the redundant addition of
`\n` since `pp` always does it nowadays.
* test/lisp/help-mode-tests.el (help-mode-tests-xref-on-pp):
Fix thinko.
* doc/lispref/help.texi (Keys in Documentation): Document it.
lisp/help-mode.el (help-make-xrefs): Implement a new \+ syntax to
inhibit buttonification.
* lisp/emacs-lisp/lisp-mode.el (lisp-el-font-lock-keywords-2)
(lisp-cl-font-lock-keywords-2): Allow single-character symbol names.
* lisp/help-mode.el (help-xref-symbol-regexp): Also match symbol
names starting with symbol syntax (bug#6601, bug#24309).
* test/lisp/help-mode-tests.el (help-mode-tests-xref-button): Test
hyperlink creation for function names without symbol syntax.
* lisp/help-mode.el: Use lexical-binding.
(help-mode-map, help-mode-menu, help-mode-setup)
(help-mode-finish): Make spelling of "Help mode" consistent throughout
the doc strings (also making it consistent with the spelling of "Help
mode" used in the Elisp manual).
(help-do-xref): Re-indent to make the else-branch easier to see.
* test/lisp/help-mode-tests.el: New file with tests for help-mode.el.
