Message 254836 - Python tracker

See Issue 224981 (bug) and Issue 403373 (patch) about the Z_SYNC_FLUSH change (the numbers in the commit message are different and do not work).

I committed my doc change to 2.7 and 3.4+, which leaves the main problem of what to do about flush(). I propose deprecate-flush.patch for 3.6, which deprecates this method.

I ran the test suite with -Werror, so I hopefully got all the instances of flush() in the library.