gdb/

gdb/
	* mi/mi-main.c (mi_cmd_execute): Use cleanup from
	prepare_execute_command.
	* top.c (prepare_execute_command): Return cleanup.
	(execute_command): Use cleanup from prepare_execute_command.
	* top.h (prepare_execute_command): Change prototype to return
	cleanup.
	* defs.h (struct value): Add opaque declaration.
	(make_cleanup_value_free_to_mark): Add prototype.
	* utils.c (do_value_free_to_mark): New function.
	(make_cleanup_value_free_to_mark): Likewise.

gdb/testsuite/
	* gdb.python/py-function.exp: Test setting a value from a function
	which executes a command.