* This simplifies later optional loading of the grid from netCDF.

* va_start, printf, fprintf, vfprintf, va_end are all candidates.

* This will later allow for decomposed and lazily-read grids.

* Also add autogenerated mark to output, prevent repeated opening of
  output for writing and shorten helper function.

* This will later allow calling this function to initialize grid
  structures not created by gridCreate.