Modifications to MultipleLocator and LogLocator, so that the locators will
give locations one past what they really need to.  This is necessary, because
in situations where round off error matters, we want the locator to offer
more that it really thinks it needs to.  The clipping of ticks still takes
place in the Axis class, so it's perfectly fine to add more locs than necessary.

In fact, matplotlib relies on the clipping behavior in the Axis class already
to not draw ticks outside of the limits of the axis.