Issue #16804: Fix 'python -S -m site' failure.

This commit fixes a bug in the 'site' module that was causing an exception
to incorrectly be thrown when running 'python -S -m site'.  The problem was
that 'USER_BASE' and 'USER_SITE' were being accessed before they were properly
initialized.  The code has been changed to use 'getuserbase' and
'getusersitepackages' instead so that the initialization always happens.
Fix pickling test in test_memoryio.

The test was closing the orginal object instead the copy. This didn't result
in visible failures because the loop range was incorrect as well.
Clarify point in name mangling doc.
Update using/mac documentation which was still on 2.5.
Clean up error messages raised by save_reduce in _pickle.
Closes #17726: small clarification in design FAQ.
Update code examples using collections.abc classes.
bind('') does not do the same as bind('localhost')
Merge heads.
Closes #13638: document PyErr_SetFromErrnoWithFilenameObject,
PyErr_SetFromWindowsErrWithFilenameObject, and
PyErr_SetExcFromWindowsErrWithFilenameObject.

Note that PyErr_SetExcFromWindowsErrWithFilenameObjectAndSomeOtherParametersSoThatTheNameGetsSoLongThatNobodyIsEverGonnaUseThisStrangeFunctionForAnything is still undocumented.
Closes #14462: allow any valid Python identifier in sre group names, as documented.
Clarify that the function *definition* creates the function and the binding in the module globals.
The Integral class does not contain implementations for the bit-shifting operations. (See #3056.)
Fix example ignoring ".svn" directories in compileall.
Issue #16550: Update the opcode descriptions of pickletools to use unsigned
integers where appropriate.  Initial patch by Serhiy Storchaka.
Merge heads.
Close issue #16163: handle submodules in pkgutil.iter_importers
Close #17702: os.environ now raises KeyError with the original environment
variable name (str on UNIX), instead of using the encoded name (bytes on UNIX).
Issue #17702: use assertRaises() for the unit test
Issue #17221: Resort Misc/NEWS.