Add (optional) Google Protocol Buffers support (example in Tutorial 3).

To use protobuf, run cmake as follows:
cmake -DUSE_PROTOBUF=1 ..
For this, protobuf library has to be installed on the system.

Further changes:
Clean up splitter/merger: default are N-to-1-merger and 1-to-N-splitter.
Fix bug in nanomsg message deallocation.
Setup proper buffer sizes for nanomsg/zeromq via cmake/bash script.
chmod +x for start scripts.

fairmq/nanomsg/FairMQMessageNN.h

@@ -35,9 +35,12 @@ class FairMQMessageNN : public FairMQMessage
 
     virtual ~FairMQMessageNN();
 
+    friend class FairMQSocketNN;
+
   private:
     void* fMessage;
     size_t fSize;
+    bool fReceiving;
 
     void Clear();
 };