Switched the batch mode kernel cache to use whatever floating point

type the rest of the code is using because otherwise it can negatively
impact the results of training.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403163

dlib/svm/pegasos.h

@@ -452,7 +452,7 @@ namespace dlib
 
             struct cache_type
             {
-                matrix<float> kernel;  
+                matrix<scalar_type> kernel;  
 
                 std::vector<long> sample_location; // where in the cache a sample is.  -1 means not in cache
                 std::vector<std::pair<long,long> > frequency_of_use;  

dlib/test/svm.cpp

@@ -369,7 +369,8 @@ namespace
         dlog << LDEBUG << "peg cached cv: " << peg_c_cv;
 
         // make sure the cached version of pegasos computes the same result
-        DLIB_TEST(sum(abs(peg_cv - peg_c_cv)) < std::sqrt(std::numeric_limits<double>::epsilon()));
+        DLIB_TEST_MSG(sum(abs(peg_cv - peg_c_cv)) < std::sqrt(std::numeric_limits<double>::epsilon()),
+                      sum(abs(peg_cv - peg_c_cv)) << "   \n" << peg_cv << peg_c_cv  );
 
         DLIB_TEST_MSG(mean(rvm_cv) > 0.9, rvm_cv);
         DLIB_TEST_MSG(mean(svm_cv) > 0.9, svm_cv);