Added an implicit conversion to unsigned long for extracting the checksum

of crc32 objects.

dlib/crc32/crc32_kernel_1.h

@@ -55,6 +55,9 @@ namespace dlib
             const std::vector<char>& item
         );
 
+        inline operator unsigned long (
+        ) const { return get_checksum(); }
+
         inline unsigned long get_checksum (
         ) const;
 

dlib/crc32/crc32_kernel_abstract.h

@@ -101,6 +101,13 @@ namespace dlib
                 - returns the current checksum
         !*/
 
+        operator unsigned long (
+        ) const; 
+        /*!
+            ensures
+                - returns get_checksum()
+        !*/
+
         void swap (
             crc32& item
         );

dlib/test/crc32.cpp

@@ -65,7 +65,7 @@ namespace
             std::vector<char> buf;
             for (int i = 0; i < 4000; ++i)
                 buf.push_back(i);
-            DLIB_TEST(crc32(buf).get_checksum() == 492662731);
+            DLIB_TEST(crc32(buf) == 492662731);
         }
     } a;