clarified a comment

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%404089

dlib/svm/function_abstract.h

@@ -28,7 +28,8 @@ namespace dlib
 
             WHAT THIS OBJECT REPRESENTS 
                 This object represents a classification or regression function that was 
-                learned by a kernel based learning algorithm.  
+                learned by a kernel based learning algorithm.   Therefore, it is a function 
+                object that takes a sample object and returns a scalar value.
         !*/
 
         typedef K kernel_type;