f:ajax Skip update model option

Hi all,

I was chatting with Alex Smirnov this week, and he pointed out that an essential
feature needed for Ajax validation is missing from the Ajax support in JSF 2.0.

When you are doing Ajax validation, you need an option to not update the backing
beans (in other words, skip the update model phase), so that *if the value is
valid*, then aren't saved to the model. I think this is sufficiently important
enough to go into the JSF maintenance release. The RichFaces syntax is like:

BTW, Ed, any updates on the MR?

Pete
#### Environment
Operating System: All
Platform: Macintosh
#### Affected Versions
[2.0]

Start by locating the existing JSF 2.0 Ajax support and its update model phase, then review how the f:ajax attributes are defined and processed. Compare the requested updateModel="false" behavior with the RichFaces syntax and existing maintenance-release discussion. Done means Ajax validation can skip updating backing beans when configured, with coverage for the valid-value case.

Written by the indexing model from the issue text.