Substantially revised the Scroller component. This version supports
the vertical,horizontalScrollPolicy properties (as in Halo) and no
longer includes a vestigal "viewportHolder" skin part. Layout is
now handled programatically, instead of with MXML constraints.

There are still some limitations for the "auto" scroll policies, and
some other minor layout problems. There is no documentation (yet).

Corrected minimum size calculation in Vertical,HorizontalLayout
for the cases where an explicit rowCount or columnCount was specified.
The measured min sizes are now only based on the first rowCount
or columnCount (visible) layout items.

QE: Scroller can now be tested
Doc: No
Checkintests: Pass
Reviewer: Ryan

Files:
modified: /flex/sdk/trunk/frameworks/projects/flex4/src/flex/layout/HorizontalLayout.as (try)
modified: /flex/sdk/trunk/frameworks/projects/flex4/src/flex/layout/VerticalLayout.as (try)
modified: /flex/sdk/trunk/frameworks/projects/flex4/src/flex/component/Scroller.as (try)
modified: /flex/sdk/trunk/frameworks/projects/flex4/src/flex/intf/IViewport.as (try)
modified: /flex/sdk/trunk/frameworks/projects/flex4/src/flex/skin/ScrollerSkin.mxml (try)