Use angle brackets (<>) rather than quotes ("") for the include
directives in our .h files. This should avoid some potentially nasty
surprises for Winelib apps.

diff --git a/include/dmplugin.h b/include/dmplugin.h
index a0c38c6..e447246 100644
--- a/include/dmplugin.h
+++ b/include/dmplugin.h
@@ -21,8 +21,8 @@
 #ifndef __WINE_DMUSIC_PLUGIN_H
 #define __WINE_DMUSIC_PLUGIN_H
 
-#include "objbase.h"
-#include "mmsystem.h"
+#include <objbase.h>
+#include <mmsystem.h>
 
 #ifdef __cplusplus
 extern "C" {