bug#19628: 25.0.50; doc of button functions

[Drew Adams]

The doc of `make-button', `insert-button', and `insert-text-button' just
mentions "a sequence of PROPERTY VALUE pairs, specifying properties to
add to the button", without saying anything about the text properties
that are special for these functions.  This is true for both the doc
strings and the Elisp manual (node `Making Buttons').

Some text properties, such as `face' and `follow-link' are common, used
generally, and are explained elsewhere.  But others, such as `action',
seem to be special to the button code and these functions.  So they
should be mentioned in this doc.

Property `action' is mentioned for function `button-activate'
(e.g. nodes `Button Properties', `Manipulating Buttons', and `Button
Buffer Commands').  But it and any other properties specific to the
button functions should be called out where we speak of such properties.
Or else such doc should refer to some location where we do specify such
properties.

What's more, the doc strings of `push-button' and `button-activate' need
to mention property `action', just as the Elisp doc for them does.  It
is not sufficient for the doc strings to simply refer to the  "normal
action" of the button, without saying what that means.


In GNU Emacs 25.0.50.1 (i686-pc-mingw32)
 of 2014-10-20 on LEG570
Bzr revision: 118168 rgm@gnu.org-20141020195941-icp42t8ttcnud09g
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --enable-checking=yes,glyphs CPPFLAGS=-DGLYPH_DEBUG=1'