Replaced C-casts with const_cast for Envelope::body_

include/amqpcpp/envelope.h

@@ -56,7 +56,7 @@ public:
      *  @param  body
      *  @param  size
      */
-    Envelope(const char *body, uint64_t size) : MetaData(), _body((char *)body), _bodySize(size) {}
+    Envelope(const char *body, uint64_t size) : MetaData(), _body(const_cast<char *>(body)), _bodySize(size) {}
 
     /**
      *  Disabled copy constructor

include/amqpcpp/message.h

@@ -103,7 +103,7 @@ protected:
         {
             // we do not have to combine multiple frames, so we can store
             // the buffer pointer in the message 
-            _body = (char *)buffer;
+            _body = const_cast<char *>(buffer);
         }
         else
         {