Default_Unexpected_Exception_Handler may leak sensitive data

[JeremyGrosser]

If a file named 500.tmplt does not exist, AWS.Server.Default_Unexpected_Exception_Handler will send the traceback from Ada.Exceptions.Exception_Information to clients, leaking information about memory offsets and program information that may be useful to an attacker trying to build an exploit.

See CWE-209 for more information about this class of vulnerability.

I believe this is unsafe default behavior and Default_Unexpected_Exception_Handler should be modified to only send Exception_Information to Log and/or Standard_Error and return a generic 500 Internal Server Error to clients.