call expressions passing the input document as an operand are not rewritten correctly

[tsandall]

For example:

package play

f(x, y) {
   x[y]
}

p {        
    input.foo = _
    f(input, "bar")        # THIS STATEMENT IS NOT REWRITTEN PROPERLY
}

Tracing shows the issue:

Enter data.play = _
| Eval data.play = _
| Index data.play = _ (matched 1 rule)
| Index data.play = _ (matched 1 rule)
| Enter data.play.p
| | Eval input.foo = _
| | Eval data.play.f(input, "bar")   # THIS STATEMENT IS WRONG
-------8< SNIP 8<---------

The last expression shown in the trace above is incorrect. The first operand (input) should have been assigned to a local variable and then substituted in the call. If the call was to a built-in function the OPA would return an error (since it would end up passing a variable to the built-in function implementation, which is illegal.)