When a client is sending a chunked request body and disconnects
between chunks, wsgi.Input.read() raises a ValueError. That's fine if
you can remember to wrap every single call to read/readline in a
try/except, but it's bad for a higher-level error handler because so
many things raise ValueError.
This adds in a new error class wsgi.ChunkReadError and raises that
instead. It inherits from ValueError so anyone catching ValueError
should continue to work.
c3ce3eef0b