add quotes (dune-common wouldn't configure otherwise)

[[Imported from SVN: r5649]]

m4/dune_common.m4

@@ -49,9 +49,9 @@ AC_DEFUN([DUNE_COMMON_CHECKS],
 	AS_HELP_STRING([--disable-tr1-headers],
 	[Prevents checking for  tr1 headers like tuple, array, etc. 
 	This might be needed for broken compilers like xlc on Blue Gene]))
-  AS_IF([test "x$enable_tr1_headers" = "xyes"],
+  AS_IF([test "x$enable_tr1_headers" = "xyes"],[
 	  AC_CHECK_HEADERS([type_traits tr1/type_traits array tr1/array tuple tr1/tuple])
-  )
+  ])
   
   AC_LANG_POP([C++])