add unit test to verify _Proxy wraps all Server methods

We have the problem that the proxy functionality requires manual
instruction on which of the Server's methods to wrap. This may cause
problems when the Server class is extended with new methods but the
_Proxy is forgotten.
This change adds a unit test to check for this case: If the Server gets
a new method the unit test will fail until the _Proxy class is fixed as
well. This certainly is not the best possible solution but for now it
ought to be enough.
MERGE W/ d6f0693e
MERGE W/ 74af835e
MERGE W/ b7f969d12283273f6e7fba23d8e2ba3aa152e90d
MERGE W/ b85f3406f1e592b994faba8903232fff2426cb32