Demo functionplotter.py range editor error

[ku-ya]

Problem Description
functionplotter.py break when auto is chosen from enum editor.
Reproduction Steps:
Run the file and change the enum to auto.
Expected behavior:
Plot disappear and raise the error

functionplotter.py:47: RuntimeWarning: invalid value encountered in double_scalars
  real_high = ceil(high/dx) * dx
/Users/ktakami/.edm/envs/chaco-dev/lib/python2.7/site-packages/chaco/data_range_1d.py:124: RuntimeWarning: invalid value encountered in greater_equal
  return ((data.view(ndarray) >= self._low_value) &
/Users/ktakami/.edm/envs/chaco-dev/lib/python2.7/site-packages/chaco/data_range_1d.py:125: RuntimeWarning: invalid value encountered in less_equal
  (data.view(ndarray) <= self._high_value))
functionplotter.py:46: RuntimeWarning: invalid value encountered in double_scalars
  real_low = ceil(low/dx) * dx
functionplotter.py:52: RuntimeWarning: divide by zero encountered in divide
  return sin(1.0/x)
functionplotter.py:52: RuntimeWarning: invalid value encountered in sin
  return sin(1.0/x)
/Users/ktakami/.edm/envs/chaco-dev/lib/python2.7/site-packages/chaco/data_range_1d.py:148: FutureWarning: elementwise comparison failed; returning scalar instead, but in the future will perform elementwise comparison
  if low == 'track':
/Users/ktakami/.edm/envs/chaco-dev/lib/python2.7/site-packages/chaco/data_range_1d.py:232: FutureWarning: elementwise comparison failed; returning scalar instead, but in the future will perform elementwise comparison
  if self._low_setting != val:
/Users/ktakami/.edm/envs/chaco-dev/lib/python2.7/site-packages/chaco/data_range_1d.py:239: FutureWarning: elementwise comparison failed; returning scalar instead, but in the future will perform elementwise comparison
  if val == 'auto':
/Users/ktakami/.edm/envs/chaco-dev/lib/python2.7/site-packages/chaco/data_range_1d.py:245: FutureWarning: elementwise comparison failed; returning scalar instead, but in the future will perform elementwise comparison
  elif val == 'track':
/Users/ktakami/.edm/envs/chaco-dev/lib/python2.7/site-packages/chaco/data_range_1d.py:285: FutureWarning: elementwise comparison failed; returning scalar instead, but in the future will perform elementwise comparison
  if self._high_setting != val:
/Users/ktakami/.edm/envs/chaco-dev/lib/python2.7/site-packages/chaco/data_range_1d.py:292: FutureWarning: elementwise comparison failed; returning scalar instead, but in the future will perform elementwise comparison
  if val == 'auto':
/Users/ktakami/.edm/envs/chaco-dev/lib/python2.7/site-packages/chaco/data_range_1d.py:298: FutureWarning: elementwise comparison failed; returning scalar instead, but in the future will perform elementwise comparison
  elif val == 'track':

OS, Python version:
OSX, Python 2.7

splits from #385