Remove unneeded continue

A continue in Connection.recv() was never executed, because it was
optimized out due to being the last statement in a loop.
Refactor TestException into a common .py file.
Parameterize max error threshold in listen()

By making the maximum error threshold in SimpleRPC.listen() derive
from a class variable, we can allow it to be modified in the test
suite, making it easier to test this particular logic.
Eliminate an unnecessary "pass" statement.
Rewrite tests for remote.py

This also includes some changes to remote.py to make constructing the
tests easier, as well as noting some lines which are not covered by
the tests.