Use explicit specialisation for numeric types and let containers

specify types as typedefs.

[[Imported from SVN: r6277]]

dune/common/bigunsignedint.hh

@@ -40,6 +40,8 @@ namespace Dune
   template<int k>
   class bigunsignedint {
   public:
+    typedef bigunsignedint real_type;
+    typedef bigunsignedint field_type;
 
     // unsigned short is 16 bits wide, n is the number of digits needed
     enum { bits=std::numeric_limits<unsigned short>::digits, n=k/bits+(k%bits!=0),