Require C++11 range-based for

Fallback support for Boost.Foreach is broken and no one has reported it.
The minimum required gcc version supports range-based for.  Recent Clang
supports range-based for.  No Microsoft compilers are supported.  Remove
support for the fallback Boost.Foreach and move the C++11 range-based
for test to the Cxx11RequiredFeature array.

SConstruct

@@ -328,6 +328,13 @@ struct %(N)s_derived : %(N)s_base {
 	array<int,2>b;
 	b[0]=1;
 '''
+),
+		Cxx11RequiredFeature('range-based for', '''
+#include "compiler-range_for.h"
+''', '''
+	int b[2];
+	range_for(int&c,b)c=0;
+'''
 ),
 		Cxx11RequiredFeature('std::unordered_map::emplace', '''
 #include <unordered_map>
@@ -1369,26 +1376,6 @@ typedef tt::conditional<false,int,long>::type b;
 		if self.check_cxx11_type_traits(context, f):
 			return
 		raise SCons.Errors.StopError("C++ compiler does not support <type_traits>.")
-	@_implicit_test
-	def check_boost_foreach(self,context,**kwargs):
-		"""
-help:assume Boost.Foreach works
-"""
-		return self.Compile(context, msg='for Boost.Foreach', successflags={'CPPDEFINES' : ['DXX_HAVE_BOOST_FOREACH']}, **kwargs)
-	@_implicit_test
-	def check_cxx11_range_for(self,context,_successflags={'CPPDEFINES' : ['DXX_HAVE_CXX11_RANGE_FOR']},**kwargs):
-		return self.Compile(context, msg='for C++11 range-based for', successflags=_successflags, **kwargs)
-	@_custom_test
-	def _check_range_based_for(self,context):
-		include = '''
-#include "compiler-range_for.h"
-'''
-		main = '''
-	int b[2];
-	range_for(int&c,b)c=0;
-'''
-		if not self.check_cxx11_range_for(context, text=include, main=main) and not self.check_boost_foreach(context, text=include, main=main):
-			raise SCons.Errors.StopError("C++ compiler does not support range-based for or Boost.Foreach.")
 	@_custom_test
 	def check_cxx11_required_features(self,context):
 		features = self.__cxx11_required_features

common/include/compiler-range_for.h

@@ -6,11 +6,4 @@
  */
 #pragma once
 
-#if defined(DXX_HAVE_CXX11_RANGE_FOR)
 #define range_for(A,B)	for(A:B)
-#elif defined(DXX_HAVE_BOOST_FOREACH)
-#include <boost/foreach.hpp>
-#define range_for	BOOST_FOREACH
-#else
-#error "No range-based for implementation found."
-#endif