Now ssh requires a tty allocation. This presents a scalability problem,
a future version could selectively allocate a tty only if typing
passwords is desired.
Sudo's tty handling is now moved into mitogen.master.
* Support passing Context() objects in function calls and return values.
Now the fakessh demo from the documentation index would work
correctly.
* Since slaves can communicate with each other now, they should also use
the same approach to unpickling as the master already used. Collapse
away all the unpickle extension crap and hard-wire just the 3 types
that support unpickling.
David Wilson