This patch extends the fork test with explicit checks for the cloned
content of the heap and RW segment as well as the seek position of an
open file descriptor. It adds the new libports/run/fork.run script
that exercises the fork mechanism implemented by the libc. It is based
on noux_fork.run, which tests the mechansim provided by noux. The
test program has been moved from ports to libports.
Issue #3478
