Merge: Removed sockets from 'debugger.nit' to put them in a new module

Removed sockets from 'debugger.nit' to put them in 'debugger_socket.nit', because it caused compilation problems for the interpreter in PNaCl.

Pull-Request: #520
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Jean Privat <jean@pryen.org>