Add get_logout_headers to request

The documentation for forget() says it is deprecated and to use get_logout_headers() on the request instead.  However, no such method has been added to the request.
Remove reference to request.get_logout_headers()
Merge pull request #1250 from dobesv/patch-2

Add get_logout_headers to request
improve timeout docs
79-char line widths!
reproduce timeout=None bug
fix timeout=None bug as well as some other potential unpacking problems
reproduce reissue_time=None bug
handle reissue_time=None properly
Merge branch 'fix.1247'
update changelog