support for system-specific scalable IO notification facilities without breaking
portability. This initial version comes with an epoll(7)-based engine for Linux
and a select(2)-based fallback engine for all other operating systems.
This required an important refactoring of the library but the external API was
preserved.
The rewrite also tries to bring the coding standards of nmap to nsock.
See http://labs.unix-junkies.org/nsock_engines.html for the details.
