Change DataType of w3c dom document

* use the underlying document implementation

still problems
09:42:00,243 ERROR eu.stratosphere.pact.runtime.task.RegularPactTask             - Error in task code:  FlatMap (de.tuberlin.dima.schubotz.fse.QueryMapper) (1/1)
org.apache.avro.AvroRuntimeException: Can't find element type of Collection
	at org.apache.avro.reflect.ReflectData.createSchema(ReflectData.java:430)
	at org.apache.avro.reflect.ReflectData.createFieldSchema(ReflectData.java:577)
	at org.apache.avro.reflect.ReflectData.createSchema(ReflectData.java:467)
	at org.apache.avro.reflect.ReflectData.createSchema(ReflectData.java:377)
	at org.apache.avro.reflect.ReflectData.createFieldSchema(ReflectData.java:577)
	at org.apache.avro.reflect.ReflectData.createSchema(ReflectData.java:467)
	at org.apache.avro.specific.SpecificData.getSchema(SpecificData.java:188)
	at org.apache.avro.reflect.ReflectDatumReader.<init>(ReflectDatumReader.java:46)
	at eu.stratosphere.api.java.typeutils.runtime.AvroSerializer.checkAvroInitialized(AvroSerializer.java:132)
	at eu.stratosphere.api.java.typeutils.runtime.AvroSerializer.serialize(AvroSerializer.java:102)
	at eu.stratosphere.pact.runtime.plugable.SerializationDelegate.write(SerializationDelegate.java:51)
	at eu.stratosphere.nephele.io.channels.SerializationBuffer.serialize(SerializationBuffer.java:130)
	at eu.stratosphere.nephele.io.channels.bytebuffered.AbstractByteBufferedOutputChannel.writeRecord(AbstractByteBufferedOutputChannel.java:170)
	at eu.stratosphere.nephele.io.RuntimeOutputGate.writeRecord(RuntimeOutputGate.java:269)
	at eu.stratosphere.nephele.io.AbstractRecordWriter.emit(AbstractRecordWriter.java:92)
	at eu.stratosphere.pact.runtime.shipping.OutputCollector.collect(OutputCollector.java:82)
	at de.tuberlin.dima.schubotz.fse.QueryMapper.flatMap(QueryMapper.java:53)
	at de.tuberlin.dima.schubotz.fse.QueryMapper.flatMap(QueryMapper.java:20)
	at eu.stratosphere.pact.runtime.task.chaining.ChainedFlatMapDriver.collect(ChainedFlatMapDriver.java:71)
	at eu.stratosphere.pact.runtime.task.DataSourceTask.invoke(DataSourceTask.java:219)
	at eu.stratosphere.nephele.execution.RuntimeEnvironment.run(RuntimeEnvironment.java:351)
	at java.lang.Thread.run(Thread.java:745)

Thanks to @rmetzger for the support