Three fixes to get this lib compiled on linux g++ 4.7.3

Added <stdexcept> include to amqpcpp.h
Removed virtual destructors for exception.h and protocolexception.h. They were causing compile issues because of (no) noexcept specification. They were empty implementations anyway, and the ~std::exception was already virtual, so they were not needed anyway.

amqpcpp.h

@@ -16,6 +16,7 @@
 #include <limits>
 #include <cstddef>
 #include <cstring>
+#include <stdexcept>
 
 // base C include files
 #include <stdint.h>

src/exception.h

@@ -22,12 +22,6 @@ protected:
      *  @param  what
      */
     explicit Exception(const std::string &what) : runtime_error(what) {}
-
-public:
-    /**
-     *  Destructor
-     */
-    virtual ~Exception() {}
 };
     
 /**

src/protocolexception.h

@@ -23,11 +23,6 @@ public:
      *  @param  what
      */
     explicit ProtocolException(const std::string &what) : Exception(what) {}
-    
-    /**
-     *  Destructor
-     */
-    virtual ~ProtocolException() {}
 };
 
 /**