extensions are installed.

during the function call setup.

This even gives a slight speedup, probably because tuple allocation
is faster than PyMem_NEW.

Functionally equivalent, clearer code, English comments.

Move the newly introduced disable_nagle_algorithm flag into the StreamRequestHandler, where it is more appropriate.

The changes in mcast.py come from the first version of the patch for issue5379.

error was thrown from itself in order to decide if the module can't be
found.  Thanks to Lucas Prado Melo for collaborating on the fix and tests.

Lib/lib-tk/test/test_tkinter/test_loadtk in order to follow the behaviour of
test_ttkguionly.