Protect against multiple includes.

diff --git a/include/psdrv.h b/include/psdrv.h
index 4126601..cfc6c34 100644
--- a/include/psdrv.h
+++ b/include/psdrv.h
@@ -1,3 +1,5 @@
+#ifndef __WINE_PSDRV_H
+#define __WINE_PSDRV_H
 
 /*
  *	PostScript driver definitions
@@ -330,6 +332,6 @@
 				  const void *bits, const BITMAPINFO *info,
 				  UINT32 wUsage, DWORD dwRop );
 
-
+#endif