Experimental feature to let apropos(1) show different keys than .Nd.

Experimental feature to let apropos(1) show different keys than .Nd.
This really takes us beyond what grep -R /usr/*/man/ can do
because now you can search for pages by *one* criterion and then
display the contents of *another* macro from those pages, like in
$ apropos -O Ox Fa~wchar
to get an impression how long wide character handling is available.