… must be prevented

The unbind callback absolutely must not raise an exception or the reactor will crash.
If there is no EM.error_handler, or if the error_handler retrows, then stop the reactor,
stash the exception in $wrapped_exception, and the exception will be raised after the
reactor is cleaned up (see the last line of self.run).

This fixes many crash reports in the 1.2 series since eventmachine#327 was merged.

…tmachine#831)

This resolves the conflict of socket bind() vs std::bind(), as more
std:: functions may be introduced in future versions of C++.

Resolves eventmachine#830