py3: port tinyproxy.py to work with Python 3
There were various str/bytes mismatches in the code. This caused
the proxy server to misbehave at run-time. The manifestation
was typically premature socket disconnect from the perspective
of the client.
Differential Revision: https://phab.mercurial-scm.org/D5951
#require docutils gettext
$ $TESTDIR/check-gendoc sv
checking for parse errors