efl: roll in first use of Eina_Cow for Evas_Object.proxy.

efl: roll in first use of Eina_Cow for Evas_Object.proxy.

Expedite biggest test memory win 100KB, average 10KB.
No slow down in proxy test (+/-3%). Speed up in most other
case (average speed up is +5%), likely due to much more
cache hit.

Elementary test show a win between 100KB to 600KB depending
on the test you are considering.

Now, you can see how I intend to use Eina_Cow and the expected
win we can have from it. I don't intend to do more for the
rest of the week so you have time to comment.

SVN revision: 82924