remote.c: Use the ptid.lwp field to store remote thread ids rather than ptid.tid.

remote.c: Use the ptid.lwp field to store remote thread ids rather than ptid.tid.

From GDB's perspective, independently of how the target really
implements threads, gdb/remote sees all threads as if kernel/system
threads.  A rationale along theses lines led to gdbserver storing
thread ids in ptid.lwp in all ports.

Because remote.c is currently using ptid.tid, we can't make gdbserver
and gdb share bits of remote-specific code that manipulates ptids
(e.g., write_ptid/read_ptid).

This patch thus makes remote.c use ptid.lwp instead of ptid.tid.

I believe that on the GDB side too, it's best that we standardize on
process_stratum targets using the ptid.lwp field to store thread ids
anyway.  The idea being leave the ptid.tid field free for any
thread_stratum target that might want to sit on top.

Tested on x86_64 Fedora 17, w/ local gdbserver.

gdb/
2014-02-19  Pedro Alves  <palves@redhat.com>

	* remote.c (remote_thread_alive, write_ptid, read_ptid)
	(read_ptid, remote_newthread_step, remote_threads_extra_info)
	(remote_get_ada_task_ptid, append_resumption, remote_stop_ns)
	(threadalive_test, remote_pid_to_str): Use the ptid.lwp field to
	store remote thread ids rather than ptid.tid.
	(_initialize_remote): Adjust.