Fixes for issues 4447, 4366.
Adds setFloat(), et al to Style, along with cross-browser abstractions
for both float and opacity.
Changes TabLayoutPanel to use the Style.setFloat(), along with a test to
ensure this causes the correct layout for tabs.
Review: http://gwt-code-reviews.appspot.com/132806

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@7399 8db76d5a-ed1c-0410-87a9-c151d255dfc7