anchor (or node) name is preceded by `info anchor' or `Info anchor' in
addition to earlier `info node' and `Info node'.
(help-make-xrefs): Adapt to new value of `help-xref-info-regexp'.
(help-make-xrefs): Only make cross-references for faces if preceded or
followed by the word `face'. Do not make a cross-reference for
variables without variable documentation, unless preceded by the word
`variable'. Update doc string accordingly.
(help-xref-mule-regexp): Don't use defconst for variables.
(help-setup-xref): Keep the last 10 elements of the stack.
(help-xref-override-view-map): New var.
(help-make-xrefs): Use it instead of building a new map each time.
(help-function-def): Allow help-fun to take a buffer as arg.
Returns the buffer-name to use for help output.
Change all the code to use it instead of hard-coding *Help*.
(help-mode-map): Put back the mouse-2 binding.
(help-xref-stack): Change the format and make buffer-local.
(help-xref-stack-item): Make buffer-local.
(help-setup-xref): Do the `push' here rather than in help-do-xref.
(help-xref-interned): Display the face doc as well.
(help-follow-mouse): Re-introduce.
(help-xref-go-back): Adapt to the new use of help-xref-stack.
(help-do-xref): Don't `push' any more.
(help-follow): Also follow face names.