casm ref --set-auto issues related to composition

[xivh]

1. casm ref --set-auto gives this message if the composition axes are changed:

  Set reference states automatically.


Error in auto_chemical_reference: Could not find enough calculated configurations
Error setting reference states automatically.

Error in auto_chemical_reference: Could not find enough calculated configurations

Changing back to the original axes solves the problem.

2. casm ref --set-auto is not finding the lowest energy when there are many structures with the same composition.

casm ref --set-auto
  Set reference states automatically.


Global chemical reference:
  Ta(1): -11.4393
  N(0.666667)Ta(0.333333): -9.4638

casm query -k formation_energy_per_atom comp_n name --verbatim
Print:
   - formation_energy_per_atom
   - comp_n
   - name

#    formation_energy_per_atom           comp_n(N)       comp_n(Va)       comp_n(Ta)                    name
                    0.05922500                    0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/14
                    -0.11890800                   0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/15
                    -0.13022100                   0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/16
                    -0.13458900                   0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/17
                    -0.13211300                   0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/18
                    -0.12255100                   0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/19
                    -0.10721800                   0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/20
                    -0.08569900                   0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/21
                    -0.05818000                   0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/22
                    -0.02482800                   0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/23
                    0.01416400                    0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/24
                    0.10875500                    0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/25
                    0.16329400                    0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/26
                    0.22268000                    0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/27
                    0.00000000                    0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/29
                    -0.04136200                   0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/30
                    -0.07484200                   0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/31
                    -0.10043200                   0.00000000  1.00000000  1.00000000    SCEL1_1_1_1_0_0_0/32