fix alamborder - missing import

Traceback (most recent call last):
  File "/Users/haikusw/chisel/fblldb.py", line 81, in runCommand
    command.run(args, options)
  File "/Users/haikusw/chisel/commands/FBAutoLayoutCommands.py", line 69, in run
    setBorderOnAmbiguousViewRecursive(keyWindow, options.width, options.color)
  File "/Users/haikusw/chisel/commands/FBAutoLayoutCommands.py", line 42, in setBorderOnAmbiguousViewRecursive
    layer = viewHelpers.convertToLayer(view)
NameError: global name 'viewHelpers' is not defined