FIX: missing color bar when direction flipped

[stevenjkern]

Closes #311. The arange produced an empty array when the direction attribute is set to flipped since mapper.low_pos > mapper.high_pos. This PR tells arange to descend when using the flipped direction rather than ascend. Here is the example from #311 before:

and after:

[cfarrow]

This does not do the right thing for flipped bounds. For example, for

low_pos = 1
high_pos = -1

this gives

array([1])

I suggest,

low = mapper.low_pos
high = mapper.high_pos
if self.direction == 'flipped':
    low, high = high, low
scrn_points = arange(low, high + 1)

and then delete lines 155-156, which would undo the bounds flip.

[jwiggins]

What about the mapper.high_pos + 1 bit? Won't that need to change when the direction is flipped as well?

[stevenjkern]

@jwiggins, I think that was covered by the change that @cfarrow suggested. Any further concerns or should I ?

[jwiggins]

Sorry, I ran into enthought/enable#266 when I was trying to test this. I've now tested it. LGTM!

[stevenjkern]

Thanks, @cfarrow and @jwiggins! Merging now.