Issue #20990: Fix issues found by pyflakes for multiprocessing.
Issue #20980: Stop wrapping exception when using ThreadPool.
Issue #20633: Replace relative import by absolute import.
Merge 3.3.
Issue #20913: make it clear that create_default_context() also enables hostname checking
#20976: remove unneeded quopri import in email.utils.
Issue #20990: Correction for 619331c67638.
Issue #19537: Fix PyUnicode_DATA() alignment under m68k.  Patch by Andreas Schwab.
tutorial: no "linux2" sys.platform on 3.x (thanks Arfrever)
Issue #21013: Enhance ssl.create_default_context() for server side contexts

Closes #21013 by modfying ssl.create_default_context() to:

* Move the restricted ciphers to only apply when using
  ssl.Purpose.CLIENT_AUTH. The major difference between restricted and not
  is the lack of RC4 in the restricted. However there are servers that exist
  that only expose RC4 still.
* Switches the default protocol to ssl.PROTOCOL_SSLv23 so that the context
  will select TLS1.1 or TLS1.2 if it is available.
* Add ssl.OP_NO_SSLv3 by default to continue to block SSL3.0 sockets
* Add ssl.OP_SINGLE_DH_USE and ssl.OP_SINGLE_ECDG_USE to improve the security
  of the perfect forward secrecy
* Add ssl.OP_CIPHER_SERVER_PREFERENCE so that when used for a server side
  socket the context will prioritize our ciphers which have been carefully
  selected to maximize security and performance.
* Documents the failure conditions when a SSL3.0 connection is required so
  that end users can more easily determine if they need to unset
  ssl.OP_NO_SSLv3.
Remove superfluous open parenthesis.  Noticed by cocoatomo on docs@.