Add support for the fork() system call. Programs that use fork must call
io_service.notify_fork() at the appropriate times. Two new examples have been
added showing how to use this feature. Refs #3238, #4162.
Clean up the handling of errors reported by the close() system call. In
particular, assume that most operating systems won't have close() fail with
EWOULDBLOCK, but if it does then set blocking mode and restart the call. If
any other error occurs we assume the descriptor is closed. Refs #3307.
EV_ONESHOT seems to cause problems on some versions of Mac OS X, with the
io_service destructor getting stuck inside the close() system call. Use
EV_CLEAR instead. Refs #5021.
Include function name in exception what() messages.
Fix insufficient initialisers warning with MinGW.
Make the shutdown_service() member functions private.
Add archetypes for testing socket option functions.