Socket: Move protocol into the socket body (as private base class) and allow non-const protocol access

Socket/Protocols/Inet: Remove not implemented  async resolv constructors (in favor of a later non-member implementation)
Socket/Protocols/Inet: More detailed exceptions thrown by INet4Address / INet6Address

* Allow empty FileHandle/SocketHandle etc instances
* Make ServerSocketHandle::listen depend on AddressingPolicy
* Replace all occurences of inet_ntoa with inet_ntop (thread safety)
* Fix handling of exceptions in ReadHelper/WriteHelper
* Fix Scheduler ERR/HUP semantics

Unified emacs Local Variables

Renaned directory satscons to senfscons

added listen to ConnectedCommunicationPolicy
added primitive doxygen documentation
cleaned up naming of some files
fixed INetProtocol.cc (missing const modifiers)
removed SocketProtcolHelper in favor of directly inheriting SocketProtocol virtually
moved implementation of TCPv4SocketProtocol virtual methods into the base classes
added rudimentary testing of the TCPv4SocketHandle protocol interface
finalized PacketSocketHandle

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