#19063: the unicode-in-set_payload problem isn't getting fixed in 3.4.
#20013: don't raise socket error when selected mailbox deleted.

I'm checking this in without a test because not much of this code
is tested and I don't have time to work up the necessary extensions
to the existing test framework.

The patch itself was tested by the person who reported the bug.
#17369: Improve handling of broken RFC2231 values in get_filename.

This fixes a regression relative to python2.