Use help-fns-short-filename in other describe- commands

Use help-fns-short-filename in other describe- commands

The commit

2015-01-16T22:52:15-05:00!monnier@iro.umontreal.ca
24b7f77581
(Improve handling of doc-strings and describe-function for cl-generic)

added 'help-fns-short-filename', which provides file name shortening
smarter than a simple 'file-name-nondirectory' call, but besides the
generic/eieio functions ('cl--generic-describe', 'cl--describe-class',
'eieio-help-constructor'), it is currently only used by
'describe-function' (via 'help-fns-function-description-header').

Make the other help commands use it, too.

(Other than the obvious consistency/maintenance argument, my immediate
motivation for this change is the possibility to customize the file
name abbreviation by advising the function.)

* lisp/help.el (describe-mode): Move to help-fns.el.  The command was
already depending on 'find-lisp-object-file-name' defined there.
* lisp/help-fns.el (describe-variable) (describe-face) (describe-keymap)
(describe-mode): Use 'help-fns-short-filename'.