* tracing in the "u" mode now works
* trace_vdelete() with wrong mode no longer break tracing
* trace_vinfo() now always returns a list of pairs of strings

tkinter.Variable class.  They replace old methods trace_variable, trace,
trace_vdelete and trace_vinfo that use obsolete Tcl commands and might
not work in future versions of Tcl.

tkapp.split() in the tkinter package.

Thanks Berker.

now.  The first argument is positional-only.

modules  can't be lazily loaded.

Thanks to Python 3.6 allowing for types.ModuleType to have its
__class__ mutated, the restriction can be lifted by calling
create_module() on the wrapped loader.

lazy-loaded module was already in sys.modules.

Thanks to Jelle Zijlstra for the code portion of the patch.

Thanks to Dusty Phillips for the initial patch.

type of __fspath__().

As part of this change, also make sure that the pure Python
implementation of os.fspath() is tested.

dictproxy was used in Python 2 and it was renamed to mappingproxy
in Python 3.3.

Patch by Julien.

Patch by Matt Morrison.

Several test cases in distutils use PyPIRCCommandTestCase as
their base class and as a result of that the following tests
were ran more than once:

* test_server_registration
* test_server_empty_registration
* test_config_interpolation

This commit moves the infrastructure used by other tests
into a new BasePyPIRCCommandTestCase class.

Patch by Yoni Lavi