only use std::integral_constant, if it conforms to the C++11 standard

C++11 requires a cast operator from integral_constant< T, v > to T. As far as I
could make out, no gcc version provides this cast in <tr1/type_traits> and only
gcc >= 4.6 provides it in <type_traits>. Therefore, the configure check now tests
for the cast operator only in <type_traits>.

Note: Our drop-in replacement conforms to the standard in the above-mentioned
sense.

[[Imported from SVN: r6992]]

dune/common/typetraits.hh

@@ -395,15 +395,11 @@ namespace Dune
   //
   // integral_constant (C++0x 20.7.3 "Helper classes")
   //
-#if defined HAVE_TYPE_TRAITS
+#if HAVE_INTEGRAL_CONSTANT
   using std::integral_constant;
   using std::true_type;
   using std::false_type;
-#elif defined HAVE_TR1_TYPE_TRAITS
-  using std::tr1::integral_constant;
-  using std::tr1::true_type;
-  using std::tr1::false_type;
-#else
+#else // #if HAVE_INTEGRAL_CONSTANT
   //! Generate a type for a given integral constant
   /**
    * \tparam T Type of the constant.
@@ -425,7 +421,7 @@ namespace Dune
   typedef integral_constant<bool, true> true_type;
   //! type for false
   typedef integral_constant<bool, false> false_type;
-#endif
+#endif // #else // #if HAVE_INTEGRAL_CONSTANT
 
   /** @} */
 }

m4/dune_tr1_headers.m4

@@ -20,6 +20,23 @@ AC_DEFUN([DUNE_TR1_HEADERS], [
      AS_IF([test "x$dune_cv_array_cplusplus0x" != "xno"],
        [AC_DEFINE([HAVE_ARRAY], 1, [Define to 1 if the <array> C++0x is available and support array::fill])
      ])
+     AC_CACHE_CHECK([whether integral_constant conforming to C++11 is supported], dune_cv_integral_constant_cplusplus11, [
+       AC_COMPILE_IFELSE([
+         AC_LANG_PROGRAM([
+           #include <type_traits>
+           void f( int );
+         ],[
+           f( std::integral_constant< int, 42 >() );
+         ])
+       ],[
+         dune_cv_integral_constant_cplusplus11=yes
+       ],[
+         dune_cv_integral_constant_cplusplus11=no
+       ])
+     ])
+     AS_IF([test "x$dune_cv_integral_constant_cplusplus11" != "xno"],[
+       AC_DEFINE([HAVE_INTEGRAL_CONSTANT], 1, [Define to 1 if std::integral_constant< T, v > is supported and casts into T])
+     ])
   ])
   AC_LANG_POP([C++])
 ])