allow arguments to be passed through to graphviz layout e.g.
allow arguments to be passed through to graphviz layout e.g.

pos=NX.graphviz_layout(G,prog='twopi',args='-Groot=a')

where a is the center node

--HG--
extra : convert_revision : svn%3A3ed01bd8-26fb-0310-9e4c-ca1a4053419f/networkx/trunk%40612

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