configure - remove the gcc option '-Wunreachable-code' because it outputs a bunch of false positives on some gcc compilers

Signed-off-by: Davide Madrisan <davide.madrisan@gmail.com>
configure - do not use AC_TYPE_SSIZE_T as it requires autoconf 2.60+

Signed-off-by: Davide Madrisan <davide.madrisan@gmail.com>
tcpinfo - use shift operations instead of simple constants in the TCP_* #definitions

Signed-off-by: Davide Madrisan <davide.madrisan@gmail.com>
NEWS - update the documentation

Signed-off-by: Davide Madrisan <davide.madrisan@gmail.com>