Building libssh2-1.2.3 on Tru64 fails at line 48 and 166 because socklen_t
isn't defined on Tru64 unless _POSIX_PII_SOCKET is defined.
This patch updates configure.ac to add -D_POSIX_PII_SOCKET when building
on Tru64 platform(s).
buildconf copies the template to example/ and configure makes sure
to generate a proper file from it and the direct_tcpip.c example
is the first one to use it - to make sure it builds fine on more
paltforms
