Use C++11 features

This reverts commit b2c2467d272359fb30f9ba6d6ee0107ad05cede0.

Some shim code was necessary to get Boost.Asio to work correctly with C++11
error handling (std::error_code, std::system_error etc.) and to get chrono
functions working properly on Clang. GCC works fine without chrono.hpp, but
Clang requires it.

Tests work correctly when compiled with GCC and Clang

Conflicts:
	include/boost/asio/dbus/functional.hpp
	test/avahi.cpp