MinGW fixes for ipaddress (part 2)

This is not a part two of the patch, it is just that I forgot to submit
the changes to ip_address.cMinGW fixes for ipaddress (part 2)

This is not a part two of the patch, it is just that I forgot to submit
the changes to ip_address.c.
Merge pull request #634 from cduclos/master

MinGW fixes for ip_address