Minor tweaks to avoid compiler warnings

dlib/dnn/cudnn_dlibapi.cpp

@@ -38,11 +38,11 @@ namespace dlib
 
     // ------------------------------------------------------------------------------------
 
-        static const cudnnTensorDescriptor_t descriptor(const tensor& t) 
+        static cudnnTensorDescriptor_t descriptor(const tensor& t) 
         {
             return (const cudnnTensorDescriptor_t)t.get_cudnn_tensor_descriptor().get_handle();
         }
-        static const cudnnTensorDescriptor_t descriptor(const tensor_descriptor& t) 
+        static cudnnTensorDescriptor_t descriptor(const tensor_descriptor& t) 
         {
             return (const cudnnTensorDescriptor_t)t.get_handle();
         }

dlib/dnn/tensor.h

@@ -219,7 +219,7 @@ namespace dlib
                     << "\n\t nr: " << nr
                     << "\n\t nc: " << nc
         );
-        DLIB_ASSERT(nr*nc == t.size() , 
+        DLIB_ASSERT(nr*nc == (long)t.size() , 
                     "\tconst matrix_exp mat(tensor, nr, nc)"
                     << "\n\t The sizes don't match up."
                     << "\n\t nr*nc:    " << nr*nc