round trip test for mirroring a neuron list
Add dotprops.neuronlist and include all dotprops methods in documentation

* dotprops.neuronlist is added as much to avoid problems
  with dispatch calling dotprops.list method
Remove call to .Internal(La_rs) by calling eigen directly

* eigen is not really much slower so long as symmetric=TRUE
  is supplied.
* this was a major blocker for a CRAN submission
Fix bug in checking extra directories in cmtk.bindir
only run test of CMTK transform of surface when cmtk available
doc: some notes on CMTK installation
make sure that xform.neuronlist is available for dispatch

* was using xform.list instead which was misbehaving!
docs: improve package introduction
roxygenise re xform.neuronlist
Bump version to 0.5.1
Merge branch 'master' of github.com:jefferis/nat

* 'master' of github.com:jefferis/nat:
  Fix loading of triangles shared between regions to assign to both regions