Fixes Issue #852.
Adds an Opera-specific implementations of getAbsoluteTop &
getAbsoluteLeft which provides more reliable results by accounting for
Opera's inaccurate scrollTop & scrollLeft on TR's and TBODY's.

Patch by: bobv
Review by: knorton



git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@1140 8db76d5a-ed1c-0410-87a9-c151d255dfc7