Updated ttcp.c to build clean for RTEMS 6 and the machines it
originally built for. Also fixed ttcp.c to close network
sockets after completion. Defined a shell command for TTCP in
rtems-bsd-shell-ttcp.c. Added TTCP to the list of RTEMS network
commands in netcmds-config.h. Added declaration of the TTCP shell
command to rtems-bsd-commands.h. Modified libbsd.py to make waf
build TTCP and its shell command.
Added the original Test TCP (TTCP) program in unmodified form.
Also added the original README for TTCP. Both the README and the
TTCP program were sourced from the first commit in the RTEMS
network demos repository.