fix #10342: make circuit an attribute of transport, rather than passing it in as method params
- also rm redundant "pass" statements, python doesn't need it if you have a docstring
rename handshake to circuitConnected, since it is just a callback and you don't *need* to do any sort of handshake
Fix bug when calling the __init__ of the base transport.
Trivial doc tweaks and ChangeLog entries for #10342.