Parenthesize macro arguments safely. I see no bug among the current

uses of PG_DETOAST_DATUM_SLICE, but it's clearly trouble waiting to
happen.

src/include/fmgr.h

@@ -11,7 +11,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/fmgr.h,v 1.53 2007/09/21 22:52:52 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/fmgr.h,v 1.54 2007/09/22 04:41:19 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -179,7 +179,7 @@ extern struct varlena *pg_detoast_datum_packed(struct varlena * datum);
 	pg_detoast_datum_copy((struct varlena *) DatumGetPointer(datum))
 #define PG_DETOAST_DATUM_SLICE(datum,f,c) \
 		pg_detoast_datum_slice((struct varlena *) DatumGetPointer(datum), \
-		(int32) f, (int32) c)
+		(int32) (f), (int32) (c))
 /* WARNING -- unaligned pointer */
 #define PG_DETOAST_DATUM_PACKED(datum) \
 	pg_detoast_datum_packed((struct varlena *) DatumGetPointer(datum))