Optimization for connected double edge swap.
Optimization for connected double edge swap.

This implements an optimization that speeds up the
`connected_double_edge_swap()` function. It uses a threshold, below
which graph connectivity is checked after each swap, and above which,
graph connectivity is only checked after a number of swaps are made.

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