MNT: add_aux_vars in fmrib config

funpack/configs/fmrib.cfg

@@ -16,6 +16,11 @@ plugin_file fmrib
 # file only contains numeric data.
 suppress_non_numerics
 
+# Auto-import auxillary variables which are
+# used in processing steps, and which would
+# otherwise not be imported.
+add_aux_vars
+
 # Only import variables from FMRIB-curated categories,
 # largely drawn from showcase categories
 category_file fmrib/categories.tsv