Added property for CircleLayout to go exactly X degrees instead of always to 360

[istrasci]

Modified CircleLayout.as to include parameter 'arcAngle'. Defaults to 360, but is settable. The items are then spread out evenly across this angle. For example, if there were 3 items with an arcAngle of 180, the items would be placed at 0, 90, and 180 degrees. There is a special case when we the arcAngle is 360 (which is the default), in that the first and last elements would overlap, but we prevent this from happening. Modified the CircleLayoutSample.mxml to include a slider for arcAngle.

Didn't mess with any versioning info. Thus, the swc in CircleLayoutSample I changed to just flexlayouts.swc. Also thought that CircleLayout* would now be more appropriate (and correct) if renamed to ArcLayout*. But I will leave all that to your discretion if you accept this request.