* thread-db.c (attach_thread): Prototype.

	* thread-db.c (attach_thread): Prototype.
	(struct private_thread_info): Remove lwpid.  Add thread handle (th),
	thread information (ti), and valid flags (th_valid, ti_valid).
	(attach_thread): Move target_pid_to_str call to after the thread
	is added to GDB's list.  Initialize the cache.
	(thread_get_info_callback, thread_db_map_id2thr)
	(thread_db_get_info): New functions.
	(thread_from_lwp, lwp_from_thread, thread_db_fetch_registers)
	(thread_db_store_registers, thread_db_thread_alive)
	(thread_db_get_thread_local_address): Use them.
	(thread_db_pid_to_str): Likewise.  Return "Missing" instead
	of calling error() for threads in unknown state.

	(clear_lwpid_callback): New function.
	(thread_db_resume): Use it to clear the cache.