it may cause OutofMemoryError in ParallelFPGrowthCombiner and ParallelFPGrowthReducer

[myn]

it may cause OutofMemoryError in ParallelFPGrowthCombiner and 
ParallelFPGrowthReducer
the code  as follow may cause OutofMemoryError  when there is lots of nodes in 
that tree;
for (Pair<List<Integer>,Long> p : tr) {
        cTree.addPattern(p.getFirst(), p.getSecond());
      }
 
so I modify this place , drop the min support nodes
 
for (TransactionTree tr : values) {
     if(cTree.getNodesTotal()>=treeNodeMax)
     {
      cTree=cTree.getTopTrees((int)(treeNodeMax*0.75));
     }
      for (Pair<List<Integer>,Long> p : tr) {
        cTree.addPattern(p.getFirst(), p.getSecond());
      }
    }