bug#1586: prefix arg when mouse clicking on header line

["Roland Winkler" <Roland.Winkler@physik.uni-erlangen.de>]

If a command takes a mouse event and an (optional) prefix arg as its
arguments, the interactive specifications are

  (interactive "e\nP")

or

  (interactive (list last-input-event current-prefix-arg))

This works fine inside the main part of a window. For a command
that does the same thing in the header line, these interactive
specifications do not work. Instead one needs, e..g,

  (interactive (list last-input-event last-prefix-arg))

i.e., current-prefix-arg needs to be replaced by last-prefix-arg.
This problem occured in the context of the command
proced-sort-header in proced.el, which provides a complete test
example. See also

http://lists.gnu.org/archive/html/emacs-devel/2008-12/msg00559.html



In GNU Emacs 23.0.60.1 (i686-pc-linux-gnu, GTK+ Version 2.14.4)
 of 2008-12-05 on regnitz
Windowing system distributor `The X.Org Foundation', version
 11.0.10502000