BatchNode does not clear batch geometries from "children" before clearing "batches"

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In the "doBatch" method, the batch geometries are not cleared from the 
"children" field before the "batches" field is cleared.

This causes batch geometries to build up after multiple calls to the "batch" 
method and meshes to linger after their geometries have been removed from the 
BatchNode.

This is because the "gatherGeometries" method relies on "batches" to determine 
which geometries in "children" are batch geometries.  Since "batches" is 
cleared but the batch geometries are not removed from "children", 
"gatherGeometries" no longer identifies these batch geometries as batch 
geometries.

Original issue reported on code.google.com by roja...@gmail.com on 12 Feb 2012 at 8:06