fix subgraph method so it only copies node attributes for nodesin the subgraph.
fix subgraph method so it only copies node attributes
for nodesin the subgraph.

Fixes #314

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extra : convert_revision : svn%3A3ed01bd8-26fb-0310-9e4c-ca1a4053419f/networkx/trunk%401557

dhimmel/networkx,kai5263499/networkx,dhimmel/networkx,kernc/networkx,jni/networkx,ghdk/networkx,jni/networkx,SanketDG/networkx,RMKD/networkx,dhimmel/networkx,kernc/networkx,blublud/networkx,debsankha/networkx,aureooms/networkx,sharifulgeo/networkx,jtorrents/networkx,aureooms/networkx,ltiao/networkx,RMKD/networkx,tmilicic/networkx,farhaanbukhsh/networkx,sharifulgeo/networkx,sharifulgeo/networkx,chrisnatali/networkx,farhaanbukhsh/networkx,beni55/networkx,dmoliveira/networkx,jakevdp/networkx,farhaanbukhsh/networkx,ionanrozenfeld/networkx,kai5263499/networkx,ghdk/networkx,ionanrozenfeld/networkx,wasade/networkx,JamesClough/networkx,dmoliveira/networkx,goulu/networkx,aureooms/networkx,yashu-seth/networkx,nathania/networkx,nathania/networkx,harlowja/networkx,michaelpacer/networkx,debsankha/networkx,bzero/networkx,jakevdp/networkx,OrkoHunter/networkx,jni/networkx,blublud/networkx,kai5263499/networkx,harlowja/networkx,kernc/networkx,dmoliveira/networkx,Sixshaman/networkx,chrisnatali/networkx,cmtm/networkx,ghdk/networkx,RMKD/networkx,bzero/networkx,andnovar/networkx,nathania/networkx,NvanAdrichem/networkx,debsankha/networkx,harlowja/networkx,ionanrozenfeld/networkx,jfinkels/networkx,bzero/networkx,jakevdp/networkx,chrisnatali/networkx,jtorrents/networkx,blublud/networkx,jcurbelo/networkx