Added a strategy to stop losing ticks on the ends of an axis.  The approach that is
used is to pad the interval that is being used to "clip" ticks from the axis because
they are off the end.

The padding is chosen specifically such that the tick cannot be drawn a pixel past the
end of the axis.  So long as the tick is within this bound, it should be OK to draw it.
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.
oops, missed a return statement in my copy/pasting.
Fixed two of the failing tests for this "Fix lost ticks" branch, and fixed a problem
in the calculation of the log tick locations.
Fix the nose failure for polar plots; don't try to pad the interval for
the theta axis of a polar plot.
Since the _get_pixel_distance_along_axis routine is supposed to return a distance
in data coordinates, it should return 0.0 instead of 0 when appropriate.
PEP8 fixes/protection try/except

PEP8 fixes, and part of a comment changed to a docstring.
Also added a try/except around each call to _get_pixel_distance_along_axis, so that
if something goes wrong with some off-beat transform, we just don't pad; things
revert back to old matplotlib behavior.
PEP8 fixes.
more PEP8 fixes.
More PEP8 fixes and comments
Pixel perturbation is now 0.5, for a more accurate calculation of exactly how
much padding to add.
Added a comment about the try/except block that catches malfunctions in
the _get_pixel_distance routines.  Also added a warning emit, so that
the try/catch at least says something if it is triggered.
Merge pull request #1686 from dhyams/fix_lost_ticks

Fix lost ticks