added missing public: qualifier.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403923

dlib/optimization/optimization_trust_region_abstract.h

@@ -60,6 +60,8 @@ namespace dlib
 
         !*/
 
+    public:
+
         // Define the type used to represent column vectors
         typedef matrix<double,0,1> column_vector;
         // Define the type used to represent the hessian matrix