to be sure that the current directory is searched

This reverts commit 0d0fa66c.

* as a container of the signals created with create_signal_wrapper.
* This makes them available to other entities via the pool.

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

Former version crashed in case of syntax error
(cf test_syntax_error.py)

The goal is to reduce the memory consumption.

  isPluged -> isPlugged.

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

pointed out by OS.

This is crucial when debugging remotely using winpdb.