#74 "fork buffer" function

[Oswald Buddenhagen]

alternative name: use file as template.
functionally identical to "select all"+"copy"+"File|
new"+"paste"

dragging this further, one could introduce real templates
as well. e.g., every new c++/h file pair in a project looks
the same: license header, for the c++ the h inclusion, for
the h the double inclusion protection. hmm, that would
require string substitutions in the template, so maybe it is
better to do this simply with a sLisp macro, provided the
necessary functions are there.