SF Patch #1463867: Improved generator finalization to allow generators

SF Patch #1463867: Improved generator finalization to allow generators
that are suspended outside of any try/except/finally blocks to be
garbage collected even if they are part of a cycle.  Generators that
suspend inside of an active try/except or try/finally block (including
those created by a ``with`` statement) are still not GC-able if they
are part of a cycle, however.