cluster doesn't start when the port parameter of listen() is a string.

[c4milo]

steps to reproduce:

1. Just use .listen('3000') instead of .listen(3000)

expected:
the service starts normally on port 3000

current result:
The service doesn't start and a socket file 3000 is created in the current path.

[rauchg]

We should probably copy the impl of net#listen, which performs conversion.

[tj]

node does that? because you can use a local sock path as well as a string, maybe they parseInt and check NaN then default to a path or something :s seems a little weird, I would expect people to parseInt() if they really want a portno

[rauchg]

i'm guessing they do port == Number(port) first

[rauchg]

https://github.com/joyent/node/blob/master/lib/net_legacy.js#L580

[rauchg]

I can see this being useful for stuff like process.env.CLUSTER_PORT