Make save/restore default feature, the configure option for save/restore removed from configure script and save/restore made available forever. All code now assume it is exists. Bochs save/restore tree previosly called "save_restore" renamed to "bochs" tree and it will be havily used everywhere, starting from save/restore and ending by various bochs debugger functions. I am going to rework debugger code to get rid of debug CPU access functions and use this "bochs" param tree instead
(TODO: find a way to call plugin_fini() for non-core devices if plugins are
disabled)
- set the device pointers back to stubs after unloading plugins
- added debug message "Exit" in all device plugin destructors
