* initialize plugin system before parsing bochsrc and command line
* pass previous value to bx_param_string_c handler
* load / unload plugin in bx_param_string_handler()
* handle user plugins after optional ones in plugin device init, reset and
save/restore functions
* added new siminterface method unregister_user_option()
* removed first version of config option handling for user plugins
* added new parameter subtree for user-defined options
* added new bx_list_c method remove()
* removed unused bx_devmodel_c method init_mem()
8aa8b1a3db