[vtkusers] Memory usage and ReleaseDataFlag

[John Biddiscombe]

>Ken recently added a list of consumers to the output data objects. Now It 
>might be possible to set up some machinery to keep track of when all 
>consumers finish with the data and then release at that point.

I noticed this and wondered the same. Shouldn't be all that difficult to 
do. simply set a flag to 1 for each consumer that has "collected" the data 
and when all are 1 release. Flags get reset to 0 when execution happens. 
(Modify ShouldIReleaseData() to check flags in consumer array)

>>An image filter outputting an image which is passed into vtkTexture can't 
>>have ReleaseDataFlag(1)


>I'm not sure about this.

I'll double check I didn't make a mistake. I was experimenting with lots of 
stuff...

JB