Patch from Van Lindberg

Patch by Martin Panter.

Patch by Alex Gaynor with some modifications by me.

Jason doced the change in the constructor *method* description, but
not the description of Request.method, so I added the change there
as well.

Issue #18978: Update docs to reflect explicitly the ability to set the attribute at the class level.

Fix #17272 - Make Request.full_url and Request.get_full_url return same result under all circumstances.
Document the change of Request.full_url to a property.

  in urllib.request.urlopen() is fixed to match the code.

I know one of them looks worse, but now it is <80 chars and
matches the 2.7 text.

Behavior confirmation and initial patch by Jessica McKellar.

It will be recalculated on sending request to HTTP server.

Patch by Alexey Kachayev

Patch by Mathias Panzenböck.

urllib.request.urlretrieve API now properly supplies a constant
non-zero block_size as it did in Python 3.2 and 2.7.  This matches the
behavior of urllib.request.URLopener.retrieve.

Issue #14780: urllib.request.urlopen() now has a `cadefault` argument to use the default certificate store.
Initial patch by James Oakley.

Issue10050 - urlretrieve uses newer urlopen. reporthook of urlretrieve takes, block number, block read size, file_size

Issue9637 - Explain in getproxies_environment that <scheme>_proxy environ variable case does not matter.