Fix issue with leaking connections when downloading remote neurons

Previously, R would run out of connections if more than 124 remote neurons
were requested from a neuronlistfh object (assuming the user had not
previously opened any connections) as the connections were not removed
properly. This is a hack around the issue, rather than a fix for the
underlying cause, but it does mean that subsets of neuronlistfh objects that
require the download of more than 124 remote neurons can now be created.
Merge branch 'hack/remoteneuronlistfh' of github.com:ajdm/nat into ajdm-hack/remoteneuronlistfh

* 'hack/remoteneuronlistfh' of github.com:ajdm/nat:
  Fix issue with leaking connections when downloading remote neurons

Conflicts:
	R/neuronlistfh.R (editing of adjacent but distinct lines)
simplify code to fix connection leak
Update NEWS
inactivate remote neuronlistfh test

* we shouldn't really be doing this as a default package test