Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Add missing include of stdio.h.

MFC after: 3 days
Sponsored by: Juniper Networks, Inc.

The following code sets up two connected TCP sockets that send data to each
other until the window is closed. Then one of the sockets is closed, which
will generate a RST once the TCP at the other socket does a window probe.

All versions of FreeBSD prior to 11/26/2004 will ignore this RST into a 0
window, causing the connection (and application) to hang indefinitely.
On patched versions of FreeBSD (and other operating systems), the RST
will be accepted and the program will exit in a few seconds.

Submitted by: Michiel Boland
Reviewed by: silby