RtlSetCurrentDirectory_U: store a handle to the current directory
along with its name.

diff --git a/include/thread.h b/include/thread.h
index 9c2ae9f..335e364 100644
--- a/include/thread.h
+++ b/include/thread.h
@@ -143,7 +143,7 @@
 
     /* the following fields do not exist under Windows */
     UNICODE_STRING  exe_str;    /* exe name string pointed to by exe_name */
-    UNICODE_STRING  curdir;     /* current directory */
+    CURDIR          curdir;     /* current directory */
     WCHAR           curdir_buffer[MAX_PATH];
 } WIN16_SUBSYSTEM_TIB;