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On 16.04, fix:
…/dynamic-graph-python-4.0.0/src/dynamic_graph/dynamic-graph-py.cc: In function 'void exposeCommand()':
…/dynamic-graph-python-4.0.0/src/dynamic_graph/dynamic-graph-py.cc:191:24: error: 'raw_function' is not a member of 'bp'
.def("__call__", bp::raw_function(dg::python::entity::executeCmd, 1), "execute the command")
^

to fix #39 also in Python2

As PyState_AddModule is not yet called in the module definition,
PyState_FindModule will not work, so for Python 3 we need to get the
module from the methods definition to retrieve a pointer to dgpyError.

Fix #39

As, from the docs:
> Passing arguments of the wrong type (e.g. passing a list when an int
> is expected) should result in a TypeError.

Thanks @jmirabel

thanks @jviereck

While here, develop test from previous commit, and fix another test in
the same file.

fix #36

This allows accessing the list of entities instanciated in the dynamic-graph.

This allows accessing the list of entities instanciated in the dynamic-graph.

  - add isPlugged and getPlugged methods,
  - add property getter name.