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.
Merge pull request #1 from TeamSpeak-Systems/gcc-fixes

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