Add namespace support for graphml reader
Modify reader so it is able to read things like:
#!xml
<node id="n1">
<data key="d0" >
<y:ShapeNode >
<y:Geometry x="2.457598996954175" y="498.06375265283157"
width="10.0" height="10.0"/>
<y:Fill color="#FF0000" transparent="false"/>
<y:BorderStyle type="line" width="1.0" color="#000000" />
<y:NodeLabel x="3.0" y="3.0" width="4.0" height="4.0"
visible="true" alignment="center" fontFamily="Dialog" fontSize="12"
fontStyle="plain" textC
olor="#000000" hasBackgroundColor="false" hasLineColor="false"
modelName="internal" modelPosition="c"
autoSizePolicy="content"></y:NodeLabel>
<y:Shape type="rectangle"/>
</y:ShapeNode>
</data>
</node>
reference thread: http://thread.gmane.org/gmane.comp.lib.boost.user/22092/focus=22092