Made the kernel objects comparable via operator==

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402364

dlib/svm/kernel.h

@@ -50,6 +50,13 @@ namespace dlib
             const_cast<scalar_type&>(gamma) = k.gamma;
             return *this;
         }
+
+        bool operator== (
+            const radial_basis_kernel& k
+        ) const
+        {
+            return gamma == k.gamma;
+        }
     };
 
     template <
@@ -128,6 +135,13 @@ namespace dlib
             const_cast<scalar_type&>(degree) = k.degree;
             return *this;
         }
+
+        bool operator== (
+            const polynomial_kernel& k
+        ) const
+        {
+            return (gamma == k.gamma) && (coef == k.coef) && (degree == k.degree);
+        }
     };
 
     template <
@@ -187,6 +201,13 @@ namespace dlib
         { 
             return trans(a)*b;
         }
+
+        bool operator== (
+            const linear_kernel& k
+        ) const
+        {
+            return true;
+        }
     };
 
     template <

dlib/svm/kernel_abstract.h

@@ -34,6 +34,8 @@ namespace dlib
                   dlib/memory_manager/memory_manager_kernel_abstract.h or
                   dlib/memory_manager_global/memory_manager_global_kernel_abstract.h or
                   dlib/memory_manager_stateless/memory_manager_stateless_kernel_abstract.h 
+                - an overloaded == operator that tells you if two kernels are
+                  identical or not.
 
         For examples of kernel functions see the following objects
         (e.g. the radial_basis_kernel).
@@ -103,6 +105,17 @@ namespace dlib
                 - returns *this
         !*/
 
+        bool operator== (
+            const radial_basis_kernel& k
+        ) const;
+        /*!
+            ensures
+                - if (k and *this are identical) then
+                    - returns true
+                - else
+                    - returns false
+        !*/
+
     };
 
     template <
@@ -203,6 +216,16 @@ namespace dlib
                 - returns *this
         !*/
 
+        bool operator== (
+            const polynomial_kernel& k
+        ) const;
+        /*!
+            ensures
+                - if (k and *this are identical) then
+                    - returns true
+                - else
+                    - returns false
+        !*/
     };
 
     template <
@@ -258,6 +281,14 @@ namespace dlib
             ensures
                 - returns trans(a)*b
         !*/
+
+        bool operator== (
+            const linear_kernel& k
+        ) const;
+        /*!
+            ensures
+                - returns true
+        !*/
     };
 
     template <