* target.h (target_ops): Change return type of detach to int.

	* target.h (target_ops): Change return type of detach to int.
	Add join.
	(join_inferior): New.
	* server.c (main): Don't skip detach support on mingw32.
	If the inferior doesn't support detaching return error.
	Call join_inferior instead of using waitpid.
	* linux-low.c (linux_join): New.
	(linux_target_op): Add linux_join.
	* spu-low.c (spu_join): New.
	(spu_target_ops): Add spu_join.
	* win32-low.c (win32_detach): Adapt to new interface.
	Reopen current_process_handle before detaching.  Issue a child
	resume before detaching.
	(win32_join): New.
	(win32_target_op): Add win32_join.