http.connection: Don't early log all exceptions.

Let handlers log exceptions at the expense of missing original traceback
info.
Use manhole to create a Unix domain socket-accessible REPL

Connect to it with:

rlwrap nc -U /tmp/manhole-PID
Never fsync... who has time for that?
Specify tornado version in setup.py
Use a beautifulsoup4 compatible with Python 3.5