Check for overlapping replication controller.

Fix #2210  @erictune 
That's disappointing - how did that end up getting merged with two strong bits of feedback like that?  


> On Nov 18, 2014, at 5:33 PM, Deyuan Deng <notifications@github.com> wrote:
> 
> In pkg/api/validation/validation.go:
> 
> > @@ -454,6 +459,17 @@ func ValidateReplicationController(controller *api.ReplicationController) errs.V
> >  	}
> >  	allErrs = append(allErrs, ValidateReplicationControllerSpec(&controller.Spec).Prefix("spec")...)
> >  	allErrs = append(allErrs, validateLabels(controller.Labels)...)
> Oh, but looks like it is still checked in in another PR 
> https://github.com/GoogleCloudPlatform/kubernetes/pull/2094/files#diff-3
> 
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