bug#22757: 25.1.50; `face-at-point` and `faces--attribute-at-point` -- add argument WINDOW-OR-BUFFER

[Keith David Bershatsky]

As a feature request, please consider adding an additional argument to 
`face-at-point` and `faces--attribute-at-point` to support WINDOW-OR-BUFFER 
with `get-char-property`; and, add that to the sections of code in said 
functions containing `get-char-property`.  The doc-strings would need to be 
updated to explain the difference.  The default would be BUFFER.

It is sometimes useful to be able to obtain a face of an overlay that is 
associated with a particular window -- e.g., an active region that may be 
different in each window.  The current functions do not have the ability to 
test for that occurrence because the third argument of `get-char-property` is 
always `nil`.

Thanks,

Keith

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In GNU Emacs 25.1.50.4 (x86_64-apple-darwin10.8.0, NS appkit-1038.36 Version 
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 of 2016-02-21 built on server.private
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