Issue 9856: Change object.__format__ with a non-empty format string from a PendingDeprecationWarning to a DeprecationWarning.

Thanks to SilenGhost for catching this.

Issue 11131: Fix sign of zero result on decimal.Decimal plus and minus operations in ROUND_FLOOR rounding mode.

fail under tracing.

arbitrarily complex expressions.  This also fixes a 3.2 regression where
operations involving negative numbers were not constant-folded.