chriseppstein/compass — pull request #1400 by lencioni (2013-10-05 13:46:53+00:00)
Title: Disable alpha transformation if opacity is 100%

IE 8 does not display overflowing content on elements that have both a z-index
and an alpha channel transformation (opacity).

Since disabling the alpha channel transformation is visually equivalent
to setting it to 100%, we may as well just disable it in these cases.