pyGridGen: removed dependency on ode.lsode and netcdf4

o Now uses ode.lsode if it's available, but falls back on
  scipy.integrate.odeint otherwise

o Uses boututils.DataFile to write NetCDF files. This
  can use netCDF4, Scientific, or scipy libraries.
pyGridGen: Some fixes and optimisations

o Fixed bug in use of closest_line to find starting
  line for gridding. opt_ri and opt_zi were used (indices)
  rather than the (r,z) coordinates

o Optimised local_gradient a little, creating spline
  objects once rather than every evaluation
Merge branch 'pygridgen'