igraph dfs may signal unreachable nodes with 0

* this still seems to be up in the air but at least some preparatory branches
 for igraph 2.0 use a 0 rather than NaN to signal unreachable nodes
* see #517

R/neuron.R

@@ -1419,7 +1419,8 @@ distal_to <- function(x, node.idx=NULL, node.pointno=NULL, root.idx=NULL,
 
 dfs_traversal <- function(x, g) {
   gdfs=igraph::dfs(g, root = x, unreachable = FALSE)
-  as.integer(gdfs$order)[!is.na(gdfs$order)]
+  # nb igraph 2.0 may change signalling for unreached nodes
+  as.integer(gdfs$order)[!(is.na(gdfs$order) | gdfs$order<1)]
 }
 
 

R/ngraph.R

@@ -539,6 +539,8 @@ prune_vertices<-function(x, verticestoprune, invert=FALSE, ...) {
   if(invert) {
     nvertices=igraph::vcount(g)
     verticestoprune=setdiff(seq_len(nvertices), verticestoprune)
+  } else {
+    verticestoprune=setdiff(verticestoprune, 0)
   }
   dg=igraph::delete_vertices(g, verticestoprune)
   # delete_vertices will return an igraph