-merge patch from Gael Guennebaud adding NumTraits for long long

and long double.
-define scalar-multiple operators only for the current Scalar type;
 thanks to Gael for expaining how to make the compiler understand
 when automatic casting is needed.
-take ScalarMultiple take only 1 template param, again.
 We lose some flexibility especially when dealing with complex numbers,
 but we gain a lot of extensibility to new scalar types.

Eigen/src/Core/NumTraits.h

@@ -87,4 +87,24 @@ template<typename _Real> struct NumTraits<std::complex<_Real> >
   };
 };
 
+template<> struct NumTraits<long long int>
+{
+  typedef long long int Real;
+  typedef long double FloatingPoint;
+  enum {
+    IsComplex = 0,
+    HasFloatingPoint = 0
+  };
+};
+
+template<> struct NumTraits<long double>
+{
+  typedef long double Real;
+  typedef long double FloatingPoint;
+  enum {
+    IsComplex = 0,
+    HasFloatingPoint = 1
+  };
+};
+
 #endif // EIGEN_NUMTRAITS_H