Move 'import' from ModExp to ModExpAtom.
Move 'import' from ModExp to ModExpAtom.

This permits syntax like:

  open import "/futlib/math"

and:

  local open import "/futlib/math"

Maybe we will make these forms mandatory.

diku-dk/futhark,HIPERFIT/futhark,diku-dk/futhark,HIPERFIT/futhark,diku-dk/futhark,HIPERFIT/futhark,ihc/futhark,diku-dk/futhark,ihc/futhark,ihc/futhark,diku-dk/futhark