Mad the include files idempotent using a consistent macro naming
scheme.

diff --git a/include/shellapi.h b/include/shellapi.h
index 90e9352..1633d72 100644
--- a/include/shellapi.h
+++ b/include/shellapi.h
@@ -1,5 +1,5 @@
-#ifndef _WINE_SHELLAPI_H
-#define _WINE_SHELLAPI_H
+#ifndef __WINE_SHELLAPI_H
+#define __WINE_SHELLAPI_H
 
 #include "windef.h"
 
@@ -274,4 +274,4 @@
 
 #include "poppack.h"
 
-#endif /* _WINE_SHELLAPI_H */
+#endif /* __WINE_SHELLAPI_H */