spacing to top and lower layers of shell. The
  coor_refine=0.1,0.15,0.1,0.2 parameters specify the radius fraction
  of the bottom layer [0], the fraction of the nodes in this layer
  [1], the top layer fraction [2], and the top layer node fraction
  [3]. I.e. the defaults will put 15% of all nz nodes into the 10%
  lower layer, 20% in the top 10% upper layer, and the rest in
  between.
  

- renamed gzipped output version with sub-directory storage ascii-gz

- built in restart facilities for temperature and tracers when using
  ascii-gz I/O with vtkio != 2


- added a composition viscosity function, CDEPV, based on two tracer
  flavors

  - for this to work, I had to move viscosity_input() *behind*
    tic_input() and tracer_input() in instructions


- added tracer_enriched option for internal heating. If tracer = on
  and tracer_enriched = on, will reader Q0_enriched and vary the element heat production 
  between Q0 for C = 0 and Q0_enriched for C = 1. I.e. this only works
  if C varies between 0 and 1.


- added an option to write from all processros to a single VTK file,
  if ascii-gz is activated, and vtkio = 2. The VTK output is of the
  "legacy", serial, single-file type, and requires that all processors see the same 
   filesystem. 

   This will lead to a bottleneck for large # of CPU computations as
   each processor has to wait til the previous is done. 

   More efficient I/O should be possible by using the distributed
   storage version of VTK, but I have no clue how this works. Anyone?