tuple.__repr__ did not consider a reference loop as it is not possible from

tuple.__repr__ did not consider a reference loop as it is not possible from
Python code; but it is possible from C.  object.__str__ had the issue of not
expecting a type to doing something within it's tp_str implementation that
could trigger an infinite recursion, but it could in C code..  Both found
thanks to BaseException and how it handles its repr.

Closes issue #1686386.  Thanks to Thomas Herve for taking an initial stab at
coming up with a solution.