C-mouse-2 elsewhere than in a buffer

["Drew Adams" <drew.adams@oracle.com>]

C-mouse-2 brings up the Text Properties menu, but only when the pointer is
over text in a buffer.

Currently, this menu uses the position of point for its position-oriented
commands, but I suggested that it might better use the pointer position. If
that were done, then there are additional, non-buffer places that could also
be accessed with the same menu.

C-mouse-2 on the mode-line runs `mouse-split-window-horizontally'.

C-mouse-2 on the vertical-scroll-bar runs `mouse-split-window-vertically'.

C-mouse-2 on the fringe is undefined.

C-mouse-2 on the header-line (e.g. Info, Buffer List) is undefined.

This question is for after the release:

How about letting C-mouse-2 always bring up the Text Properties menu? The
mode-line, header-line, and fringe are now places that have a foreground and
background property, IIUC. Why not let users use the Text Properties menu to
interrogate and change those properties? (The current menu code might not
work on these areas, but perhaps it could be made to work there.)

There would be no conflict with existing bindings, apart from
`mouse-split-window-*', which could be bound instead to C-mouse-1 or
C-mouse-3 or M-mouse-* or S-mouse-*.