Re-working @UiField and Widget replacement to use DOM walking rather then IDs.

Microbenchmarks show ~10% speedup in Firefox/Webkit browsers.   AdWords saw little change on Firefox and potential 3% improvement in startup time on chrome.

Some additional constraints on UiBinders:
+ To simplify handling of paragraph, we disallow block-level fields and inside of <p> elements.
+ TD tags MUST be withing a TR to simplify DOM walking.

Review at http://gwt-code-reviews.appspot.com/241801

Review by: rjrjr@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@7816 8db76d5a-ed1c-0410-87a9-c151d255dfc7
27 files changed