formula-based df/call's do not work with hpc_args

[mschubert]

Standard calls work both by specifying hpc args or not (i.e., serial or hpc module processing)

For formula-based indices, this does not work because index references variables in args.

This most likely needs subsetting of the IndexedFormula@args variable back to IndexedFormula@index.

> st$lm(Sepal.Width ~ Sepal.Length, data=iris)
  Sepal.Width Sepal.Length         term   estimate  std.error statistic
1           1            1 Sepal.Length -0.0618848 0.04296699 -1.440287
    p.value size
1 0.1518983  150
> st$lm(Sepal.Width ~ Sepal.Length, data=iris, hpc_args=list())
# Error in (function (` fun`, ..., more.args = list(), export = list(),  :
#   Argument required but not provided: data ...

[mschubert]

fixed in e58679a