Titov and Demoulin test cases
-----------------------------

Refer to 2012SoPh..278..347V (Low-Hft case) for more information

Twist test
----------
        File            a      q [10^12]   Twist (/pi)
                 
1) td_N01_0.06.sav    0.31*d     100        -6.054   
2) td_N05_0.06.sav    0.8*d      100        -2.114   
3) td_N1_0.06.sav     0.8*d       29.5      -1.004   
4) td_N3_0.06.sav     0.8*d        5.5      -0.201   

1-4 are on a 107x171x79 nodes grid

Resolution test
---------------
As case 3) above but on differenr grid
      File          delta    nx    ny   nz   Twist (/pi)    
                   
5) td_N1_0.03.sav    0.03   209    337  153     -2.15       
6) td_N1_0.12.sav    0.12    56     88   42     -2.09  


All cases are  discretizing the same physical volume
       x:      -3.18000      3.18000
       y:      -5.10000      5.10000
       z:       0.00000      4.56000
at all resolutions