bar_setFaceAlpha

Set the FaceAlpha property of BAR and BARH objects

This is a simple workaround for the fact that Matlab's BAR and BARH
plotting functions do not pass the 'FaceAlpha' property to the actual
plotting functions.
Usefully, e.g.
* in case you want to have the grid lines shine through the bars
* in general in case you want to have some graphics behind your
bars
* or, in case you simply prefer the faced out colors.

Hopefully, this function gets obsolete in some future Matlab release.