betweenness dict in edge_betweenness should only contain two-tuples
betweenness dict in edge_betweenness should only contain two-tuples

Fixes #159

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extra : convert_revision : svn%3A3ed01bd8-26fb-0310-9e4c-ca1a4053419f/networkx/trunk%40834

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