net: give better error messages

Add address and/or port to errors where applicable for better reporting.

See joyent/node#7005 and #16 
I'm not sure if that's a good idea.  If the options object has a 'stack' or 'message' property, it will override the property of the same name on the exception object.

Aside, when an errno is not recognized by libuv, that's generally a bug.  No need to call it out here, it might lull people into thinking it's okay.