This work extends AIStateMachine to run multiplex() in the thread
that calls run(), cont() or set_state(). Note that all three
eventually call locked_cont(), so thats where multiplex() is called
from. Calling multiplex() means "running the state machine", as in
"calling multiplex_impl".
Currently only LLURLRequest uses this feature, and then only
for the HTTPGetResponder, and well only for the initializing,
start up and normal finish states.
A current/remaining problem is that we run into a situation where
the curl thread runs a statemachine to it's finish and kills it,
while the main thread is also 'running' it and tries to call
multiplex while the statemachine isn't running anymore.
mTotalBytes had the meaning of "the sum of all elements in the vector",
but was reset to 0 at the start of a transaction. The meaning is now
changed to "total number of bytes in the vector that belong to the
current transaction".
