Fix includes right throughout the Xserver tree:

change "foo.h" to <X11/foo.h> for core headers, e.g. X.h, Xpoll.h;
change "foo.h", "extensions/foo.h" and "X11/foo.h" to
    <X11/extensions/foo.h> for extension headers, e.g. Xv.h;
change "foo.[ch]" to <X11/Xtrans/foo.[ch]> for Xtrans files.

Xext/sleepuntil.c

@@ -30,8 +30,8 @@ in this Software without prior written authorization from The Open Group.
 /* dixsleep.c - implement millisecond timeouts for X clients */
 
 #include "sleepuntil.h"
-#include "X.h"
-#include "Xmd.h"
+#include <X11/X.h>
+#include <X11/Xmd.h>
 #include "misc.h"
 #include "windowstr.h"
 #include "dixstruct.h"