Odd bug with ast and strutils.

[solo989]

If you run this code with code with strutils imported the input arg is treated 
as typed instead of untyped. 
    
    
    import macros
    import strutils
    
    macro replace(input: untyped, before: untyped, after: untyped) : untyped =
      echo treeRepr input
      echo treeRepr before
      echo treeRepr after
    
    
    var x = 10
    var y = 20
    
    replace do:
      for i in 0..5:
        x += 5
        y += 15
    do:
      x += 5
      y += 15
    do:
      x += 5
    
    echo x
    echo y
    

but if instead you comment out strutils input goes back to being untyped. 
nnkIdents become nnkSyms instead of staying as nnkIdents.