issue13183 - Fix pdb skipping frames after hitting a breakpoint and running step. Patch by Xavier de Gaye

Issue #14664: It is now possible to use @unittest.skip{If,Unless} on a test class that doesn't inherit from TestCase (i.e. a mixin).

Issue #14632: Updated WatchedFileHandler to deal with race condition. Thanks to John Mulligan for the problem report and patch.

the links were not located in an archive subdirectory.

This also alters the fix to #11603. Specifically, setting __repr__ to
object.__str__ now raises a recursion RuntimeError when str() or repr() is
called instead of silently bypassing the recursion. I believe this behavior is
more correct.

Patch by Dionysios Kalofonos.

Original patch by Peter Otten.