Also export the number type as 'field_type'

I can't make up my mind whether I want 'ctype' or 'field_type'

[[Imported from SVN: r9447]]

dune/gfe/rigidbodymotion.hh

@@ -26,6 +26,7 @@ public:
 
     /** \brief The type used for coordinates */
     typedef T ctype;
+    typedef T field_type;
 
     /** \brief The type used for global coordinates */
     typedef Dune::FieldVector<T,embeddedDim> CoordinateType;

dune/gfe/unitvector.hh

@@ -64,6 +64,7 @@ public:
 
     /** \brief The type used for coordinates */
     typedef T ctype;
+    typedef T field_type;
 
     /** \brief The type used for global coordinates */
     typedef Dune::FieldVector<T,N> CoordinateType;