Outdated comment for bson.NewObjectId

[Dmitry Chestnykh]

This doc-comment is no longer true, since readMachineId is called when initializing module:

// This function causes a runtime error if it fails to get the hostname
// of the current machine.

http://bazaar.launchpad.net/~niemeyer/mgo/v2/view/head:/bson/bson.go#L218

Also, in another comment readMachineId is called initMachineId:

// initMachineId generates machine id and puts it into the machineId global
// variable. If this function fails to get the hostname, it will cause
// a runtime error.
func readMachineId() []byte {

http://bazaar.launchpad.net/~niemeyer/mgo/v2/view/head:/bson/bson.go#L197

[Dmitry Chestnykh (dmitry-codingrobots)]

Another, unrelated, mistake in comment:
http://bazaar.launchpad.net/+branch/mgo/v2/view/head:/gridfs.go#L378

(Stray "It is a runtime")

[Gustavo Niemeyer (niemeyer)]

All fixes adopted. Thanks Dmitry.