[CM] Idea: using handles instead of pointers, s7_clone

[bil at ccrma.Stanford.EDU]

I just noticed your s7_clone is not necessarily making a new
s7 instance -- in this case you'll have two views into
one s7; if these are in separate threads, the two s7's
will be colliding in their use of the evaluator -- it
is not thread safe in the sense that any number of
threads can be calling into the same s7 instance.
There's a note about this in s7.html.  And if they aren't
in separate threads, you've gained nothing by copying
the array of handles, unless I'm missing something.