invalid NSE warning when using full path to variable

[zachary-foster]

> x = mutate_obs(obj, "occ_AUT", obj$data$tax_occ$AUT)
Adding a new "integer" vector of length 365.
Warning message:
Ambiguous names used in non-standard evaluation:
   AUT
These could refer to values in different datasets with the same name. The following values will be used:
   data$tax_occ$AUT

This should not use NSE, since the path to the full variable is supplied.