Support Windows on node >= 0.11.14

Clustering dgram sockets isn't supported on Windows, and can't be
disabled until node 0.11.14. When dgram is clustered, node crashes.
After 0.11.14 we can request dgram sockets not be clustered by using the
new exclusive option to bind.
Merge pull request #7 from strongloop/use-exclusive

Support Windows on node >= 0.11.14