Update pydot interface to use multigraph and handle edge attributes the same way as pygraphviz interface.
Update pydot interface to use multigraph and handle edge attributes
the same way as pygraphviz interface.

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extra : convert_revision : svn%3A3ed01bd8-26fb-0310-9e4c-ca1a4053419f/networkx/trunk%401100

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