-trace-define-variable and -trace-list-variables.

    	* tracepoint.c (create_trace_state_variable): Make
    	private copy of name, as opposed to assuming the
    	pointer lives forever.
    	(tvariables_info_1): New.
    	(tvariables_info): Use the above.
    	* tracepoint.h (create_trace_state_variable, tvariables_info_1):
    	Declare.
    	* mi/mi-cmds.c (mi_cmds): Register -trace-define-variable
    	and -trace-list-variables.
    	* mi/mi-cmds.h (mi_cmd_trace_define_variable)
    	(mi_cmd_trace_list_variables): New.
    	* mi/mi-main.c (mi_cmd_trace_define_variable)
    	(mi_cmd_trace_list_variables): New.