Add a new bindresvport_sa() function to cleanup the code.

Hi,

while testing MIT Kerberos with socket_wrapper (see http://cwrap.org ), Nalin an I stumbled upon the bindresvport() code which only works with IPv4 addresses correctly. As I implemented support for bindresvport() in socket_wrapper I did it with a piece of code which is more portable. So I've implemented it in MIT Kerberos too. It allows to us to work on IPv4 and IPv6 addresses and check return values correctly.

I'm new to MIT Kerberos. I try to adopt the coding style. Comments are welcome!