call: set mTag in setter
icp: added ping request/response
build: require protobufc

* added support for freerds specific cmake modules
* added FindProtobufC detection script
Initially added pbrpc

pbrpc is a simple bidirectional, rpc mechanism that uses protocol buffers for
serialization/deserialization.
Added script to compile protobuf files for c/c++
Initial version of icp

The internal communication protocol is used to communicate with session-manager.
As transport currently protocol buffers over a named pipe are used.
rds: start/stop icp thread
rds: use icp to query if a channel is allowed
rds: print waiting for session-manager message