Use ptid_t.tid to store thread ids instead of ptid_t.pid.

	Use ptid_t.tid to store thread ids instead of ptid_t.pid.

	* gnu-nat.c (inf_validate_procs): If this is the first time we're
	seeing a thread id, extend the main thread's ptid.  If we still
	have pending execs, don't be verbose about new threads.
	(gnu_wait, gnu_resume, gnu_attach, gnu_thread_alive)
	(gnu_pid_to_str, cur_thread, sig_thread_cmd): Adjust.
	* i386gnu-nat.c (gnu_fetch_registers, gnu_store_registers):
	Adjust.