Audit __getstate__ and __setstate__ methods

[corranwebster]

There are a number of Chaco classes which override __getstate__ and possibly __setstate__. Most of these seem to be removing traits from the state dict, which is now correctly handled by marking those traits as transient.

For example:

chaco/chaco/lineplot.py

Lines 415 to 421 in e342361

	def __getstate__(self):
	state = super(LinePlot,self).__getstate__()
	for key in ['traits_view']:
	if key in state:
	del state[key]
	return state

This is removing the traits_view trait from the state - under normal Traits, this will never be in the state because of special handling of Views, so this whole method can be removed.

Another example:

chaco/chaco/grid.py

Lines 413 to 419 in e342361

	def __getstate__(self):
	state = super(PlotGrid,self).__getstate__()
	for key in ['_cache_valid', '_tick_list', '_tick_positions', '_tick_extents']:
	if key in state:
	del state[key]
	return state

Here the traits _cache_valid, _tick_list, _tick_positions, _tick_extents are being removed from the state. These traits should be marked with transient=True metadata and then the __getstate__ method can be removed.

If it turns out that there are necessary things being done in a __getstate__, we should make sure that there is a super call.