Add cutoff parameter to dijkstra algorithms.  More memory efficient version of dijkstra_path_length algorithms by not computing paths. Addresses #500
Add cutoff parameter to dijkstra algorithms.  More memory efficient version of dijkstra_path_length algorithms by not computing paths.
Addresses #500

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