move some static thread state into remote_state

move some static thread state into remote_state

This moves a few static variables from thread-info functions into
remote_state.  Pedro said on irc that these functions implement the
ancient thread-discovery method and that he wouldn't be surprised if
they had rotted; nevertheless it seems safer to me to make them
explicitly per-remote.

This necessitated moving a couple of macros and a typedef earlier in
the file.

	* remote.c (struct remote_state) <echo_nextthread, nextthread,
	resultthreadlist>: New fields.
	(OPAQUETHREADBYTES, threadref, MAXTHREADLISTRESULTS): Move earlier.
	(remote_get_threadlist, remote_threadlist_iterator): Use
	new fields.  Remove static variables.