Add secondary sort option for topological sort
Add secondary sort option for topological sort

Fixes #174

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extra : convert_revision : svn%3A3ed01bd8-26fb-0310-9e4c-ca1a4053419f/networkx/trunk%40831

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