_FD_LOCK/UNLOCK() is libpthread specific and not needed for librthread, so

isolate its usage to libpthread only and replace with generic non-static
mutex support in the one place it is needed:
- remove _FD_LOCK/UNLOCK from lseek and ftruncate in libc and make the
functions weak so that libpthread can override with its own new
versions that do the locking.
- remove _thread_fd_lock/unlock() weak functions from libc and adjust
libpthread for the change.
- add generic _thread_mutex_lock/unlock/destroy() weak functions in libc
to support non-static mutexes in libc and add libpthread and librthread
implementations for them. libc can utilize non-static mutexes via the
new _MUTEX_LOCK/UNLOCK/DESTROY() macros. Actually these new macros can
support both static and non-static mutexes but currently only using
them for non-static.
- make opendir/closedir/readdir/readdir_r/seekdir/telldir() thread-safe
for both thread libraries by using a non-static mutex in the struct
_dirdesc (typedef DIR), utilizing it in the *dir functions and remove
remaining and incorrect _FD_LOCK/UNLOCK() use in libc.
- add comments to both thread libraries to indicate libc depends on the
current implementation of static mutex initialization. suggested by
marc@
- major bump libc and libpthread due to function removal, structure
change and weak symbol conversions.
okay marc@, tedu@

src/include/dirent.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: dirent.h,v 1.17 2007/02/08 16:34:38 millert Exp $	*/
+/*	$OpenBSD: dirent.h,v 1.18 2007/06/05 18:11:48 kurt Exp $	*/
 /*	$NetBSD: dirent.h,v 1.9 1995/03/26 20:13:37 jtc Exp $	*/
 
 /*-
@@ -71,6 +71,7 @@ typedef struct _dirdesc {
 	long	dd_rewind;	/* magic cookie for rewinding */
 	int	dd_flags;	/* flags for readdir */
 	struct _telldir *dd_td; /* telldir position recording */
+	void	*dd_lock;	/* mutex to protect struct */
 } DIR;
 
 #define	dirfd(dirp)	((dirp)->dd_fd)