c_osx.py: extension to copy local frameworks

The extension relies on a new 'copytree' method in Build class
+ccnx, ice_cxx, ns3, ns3_runner
New extra: monogodb detector
extras/doxygen: Extending module and refactoring configuration phase

Now, doxygen.py doesn't attempt to check existence of the doxygen and
tar programs as soon as module is loaded in configuration phase.
Instead, wscript need to explicitly run check_doxygen, with optional
parameters.  This way it is possible to specify mandatory=False flag,
without resorting to exception handling