Compile with GLEW < 1.9.0 compiler-warning fixes

* fixing defined but unused warnings
fix multicasttest compiler warnings

* signed/unsigned comparison fix
* also use appropiate integer type which allows errorcodes
Add missing include in vvtcpserver.h

* previous removal of vvTcpServer.h-include cauzed unknown variable
  types
* include vvsocket.h in order to have sockaddr_in and socklen_t
  available again

Note:
  A move of includes from vvsocket.h to vvplatform.h might be
  meaningfull in order to reduce dependencies of the big header
  vvsocket.h and only include vvplatform.h instead.

Recommendation:
  Always build test-programs to avoid future errors of this type.
Set in Preferences renderer dialog as default

* default widget is set by <property name="currentIndex">