They now return NotImplemented for unsupported type of the other operand.

The recursive frame pruning code always undercounted the number of elided frames
by one. That is, in the "[Previous line repeated N more times]" message, N would
always be one too few. Near the recursive pruning cutoff, one frame could be
silently dropped. That situation is demonstrated in the OP of the bug report.

The fix is to start the identical frame counter at 1.

In the documentation for the traceback module, the definitions of functions
extract_tb(), format_list() and classmethod StackSummary.from_list()
mention the old style 4-tuples that these functions used to return or accept.

Since Python 3.5, however, they return or accept a FrameSummary object
instead of a 4-tuple, or a StackSummary object instead of a list of 4-tuples.

Co-Authored-By: Berker Peksag <berker.peksag@gmail.com>

* Replaced list(<generator expression>) with list comprehension
* Replaced dict(<generator expression>) with dict comprehension
* Replaced set(<list literal>) with set literal
* Replaced builtin func(<list comprehension>) with func(<generator
  expression>) when supported (e.g. any(), all(), tuple(), min(), &
  max())

This fixes a regression caused by revision 73afda5a4e4c. Also reverts the
decimal test workaround added in revision 5f3dd0a2b1ab.

Remove test_without_exception(). According to revision ecaafc32c500, this was
added in Python 2 so that print_exc() would output “None” when called with no
exception set. However print_exc() never worked like this in Python 3, and
the use case is not documented.

Restore TracebackCases class name (instead of SyntaxTracebackCases), because
the class also tests other exceptions.