Re-work gffi finalization to remove mandatory return value boxing

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GFFI return values are currently boxed to allow a .finalizeWith() method on
all return types, including primitives.

This has caused a host of small bugs because the programmer's mental model
is broken.  It also complicates the ability to finish the removal of
CFunction.call.  Essentially, we are constantly paying the mental/overhead
penalty of boxed types and very rarely seeing the benefit.

Suggest we move away from

var fd = _open.call("filename", O_RDWR);
fd.finalizeWith(_close, fd);

and toward something like

var fd = _open("filename", O_RDWR);
fd = gffi.finalizeWith(fd, _close, fd);

This forces a re-write of fd into a boxed type, insuring that the
programmer knows exactly what's going on -- potentially allowing code like
this:

this.fd = _open("Filename", O_RDWR);
this._fd_gcRoot = gffi.finalizeWith(null, _close, this.fd);

...and perhaps finalizeWith is now less appropriate than, say, "new
gffi.finalizingBox()".

Original issue reported on code.google.com by wes%page...@gtempaccount.com on 4 May 2010 at 3:42

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Original comment by wes@page.ca on 5 Sep 2012 at 3:23