goal_eval_unint doesn't work with take and drop

[brianhuffman]

Here's what happens if you try:

sawscript> prove do { goal_eval_unint ["take"];} {{ \ (x : [8]) -> take`{2} (x ^ x) == take`{2} x ^ take`{2} x }}

Stack trace:
"prove" (<stdin>:1:1-1:6):
"goal_eval_unint" (<stdin>:1:12-1:27):
could not create uninterpreted function argument of type PrimName {primVarIndex = 135, primName = Prelude.Nat, primType = sort 0}

[brianhuffman]

Also, that PrimName {primVarIndex... nonsense in the error message needs to be fixed.