Fix compilation of streaming nested Array, i.e., cout << Array<Array<>>
(grafted from b27d432812bad681cedd844872ca2c85e169630c)

--HG--
branch : 3.3
extra : source : b27d432812bad681cedd844872ca2c85e169630c
diff --git a/Eigen/src/Core/NumTraits.h b/Eigen/src/Core/NumTraits.h
index dd61195..daf4898 100644
--- a/Eigen/src/Core/NumTraits.h
+++ b/Eigen/src/Core/NumTraits.h
@@ -215,6 +215,8 @@
   static inline RealScalar epsilon() { return NumTraits<RealScalar>::epsilon(); }
   EIGEN_DEVICE_FUNC
   static inline RealScalar dummy_precision() { return NumTraits<RealScalar>::dummy_precision(); }
+
+  static inline int digits10() { return NumTraits<Scalar>::digits10(); }
 };
 
 template<> struct NumTraits<std::string>