Implement -var-info-path-expression.

	Implement -var-info-path-expression.

	* mi/mi-cmds.h (mi_cmd_var_info_path_expression):
	Declare.
	* mi/mi-cmds.c (mi_cmds): Register var-info-path-expression.
	* mi/mi-cmd-var.c (mi_cmd_var_info_path_expression): New.
	* varobj.c (struct varobj): New field 'path_expr'.
	(c_path_expr_of_child, cplus_path_expr_of_child)
	(java_path_expr_of_child): New.
	(struct language_specific): New field path_expr_of_child.
	(varobj_create): Initialize the path_expr field.
	(varobj_get_path_expr): New.
	(new_variable): Initialize the path_expr field.
	(free_variable): Free the path_expr field.
	(adjust_value_for_children_access): New parameter
	WAS_TYPE.
	(c_number_of_children): Adjust.
	(c_describe_child): New parameter CFULL_EXPRESSION.
	Compute full expression.
	(c_value_of_child, c_type_of_child): Adjust.
	(cplus_number_of_children): Adjust.
	(cplus_describe_child): New parameter CFULL_EXPRESSION.
	Compute full expression.
	(cplus_name_of_child, cplus_value_of_child)
	(cplus_type_of_child): Adjust.
	* varobj.h (varobj_get_path_expr): Declare.