Find how many downstream partners tracers have connected up

Remove points from a neuron, keeping the root node intact

downstream.deletion.test(someneuronlist, names = c("Alex Bates",
  "Ruairi Roberts"), ...)

Arguments

someneuronlist	a neuronlist object. Should be the downstream partners of (a) neuron(s) of interest
names	Full names of tracers to consider
...	additional arguments passed to methods.

The percentage of downstream singlet nodes named tracers have contributed to neuron in