BUG: Fixes issue #966. When appending the new axes, there is a bug where it
does not account for the reference horizontal locator index when adding
a veritcal axes and does not accout for the reference vertical locator
index when adding a horizontal axes. This fixes that bug so that the
append_axes function adds the axes where it is expected.
TST: Added test case for the divider_append method of axes_grid1 module