"after" variable watchers

[martin rudalics]

I'd like to install the attached patch which expands on the existing
variable watching mechanism in the sense that the variable whose value
gets changed has already the new value assigned to within the body of
the watch function.  Such a feature is useful when the watch function
calls already existing functions which act upon the variable's new value
in a possibly deeply nested fashion.

Consider the following example: A user wants to set `right-margin-width'
of a buffer and I want to decide whether that margin really fits.  The
mechanism whether it fits would be nested in a common function that
decides whether any decoration (fringe, scroll bar, margin) fits into
any window showing that buffer based on the minimum sizes of that window
and the sizes of the remaining decorations.  Passing a "this is the
requested new value of the right margin" setting to such a function is
awkward at the very least.

Objections, suggestions, comments?

Thanks, martin

after-variable-watchers.diff
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