This is the version from the Comprehensive C Archive Network, licensed
under the CC0 "No Rights Reserved" Creative Common License.
http://ccodearchive.net/info/isaac.html
For platforms that read from the system's random number generator,
reseed during level change, before the map of a new level is created and
after level creation has finished.
Linux and BSD system have random number source devices that can be used
as source for a unguessable seed source.
Other platforms fall back to generate the seed with gettime().
Patric Mueller