* add ipv6 support by setting address family

* Use is_alive instead of isAlive for Python 3.9 compatibility.

* Use encodebytes instead of deprecated encodestring.

* Fix Python 2 and 3 compatibility for base64.

On Python 3, socket.makefile() returns an object with a tell() method, but one that always raises io.UnsupportedOperation.

httpservers writes an empty string or an internal server
error message, these needs to be bytes in python 3.

It might have been useful to have wsgi_write_chunk accept
either bytes or strings and do the right thing, but that
seemed too invasive to be safe.

This reverts commit 78dd2ec0138467305f1686558fca4ff8ca0b2b70.

That removes the use of the so-called "thread safe" tsafe module, which
adds a lock around many messages, but did not account for the use of
that lock in the paste/httpserver.py module.

An attempt was made to just get rid of that lock, but since there is
limited testing of that area, and few resources to confirm the change,
it's been decided that keeping tsafe and allow the deprecation warning
to be exposed is the best thing to do. With luck the decpration warning
will encourage people to not use the httpserver and choose something
else instead.

Fixes #19