Improve error message.
some test.0xdata fixs
a little better handling of glm2 grid
didn't push this
playing with effects of different enum mappings
corrected index used in shuffled OOB array for VI
Patch up variable importance handling.
Refer to .variables in variable_importances when available instead of the model's column names.
Don't rely on max_var: variable list is not truncated, so truncate after sorting.
PP-103