Refactor reading of commands

	Refactor reading of commands

	* defs.h (read_command_lines_1): Declare.
	* cli/cli-script.c (read_next_line): Only return string,
	do not process.
	(process_next_line): New, extracted from read_next_line.
	(recurse_read_control_structure): Take a function pointer to the
	read function.
	(get_command_line) Pass the read_next_line as reader function
	into recurse_read_control_structure.
	(read_command_lines_1): New, extracted from...
	(read_command_lines): ...here.