Morgan reorganized and rephrased parts of the intro.  I added two sources, one of which is not compiling properly, and corrected a few typos.
Initial commit of contract.vertices.practice.R.  This code is practice to try to take a shapefile into igraph and contract it such that nodes exist only at intersections, but the lengths of roads are maintained.
Fixed this practice code so that it takes a practice network and collapses it such that nodes are only present at terminal points and intersections.  It does this without damaging existing connections or edge lengths.
Added a call to dlg.contract.vertices.  This takes the data frame edge.df and returns a new data frame with all the nodes of degree 2 removed (in other words, there are only nodes at terminal points and intersections).
Initial commit of dlg.contract.vertices.R.  This is the final code based on contract.vertices.practice.R.  It takes edge.df from shapefile_to_network program and returns a new data frame with all the nodes of degree 2 removed.
Fixed downstream problems due to using new network from dlg.contract.vertices.  There are still some issues: 1) For some reason, I can't plot the most central nodes.  It throws some error about indexes being out of bounds.  Right now that code is commented out, since it's not strictly necessary.  2)  There's an error being thrown on line 239 for some of the files.  Specifically, Foraging3_Network and Andersen_Roads (so far).  It says that there are invalid vertex names... perhaps this code doesn't work so well for graphs that have disconnected parts?