All languages: Using uint64 for RemoteServer call return values

Recent addition of IntegerConverter in rsb0.14 seems flaky (it
seems Python will always send 64bit, and no conversion can be made),
-> now using 64bit types for transport everywhere revision numbers
are exchanged as an RPC result, i.e. all RemoteIU modifications
and ResendRequests (Also disabled our own legacy IntConverters).

Note: the ipaaca.proto Protobuf definition has not been changed,
for compatibility reasons. Java version contains explicit (int)
casts when protobuf objects are built. (TODO Discuss proto->64bit)

Tests between all three languages work (Netboot, rsb0.14,
protobuf2.6.1, spread4.4), tested with WOz+Cere+Billie.