ng:class{,-odd,-even} shouldn't reset element classes

[groner]

ng:class remembers the classes present at compile time and resets the target element's classes whenever $eval() is run. Any other classes that have been added or removed since the element was compiled are reset.

I have prepared an example showing how this breaks the jQueryUI selectable widget.
http://jsfiddle.net/gronky/XsHqL/

[IgorMinar]

Instead of remembering what classes were applied to an element during the compile time, we should do the following:

• if model value changed do the following, otherwise skip
• check the DOM and read all classes applied to the element
• add/remove our class to/from the string
• push the class string to the DOM

[IgorMinar]

This issue wasn't completely fixed. The original test case still doesn't work because of: #473

[IgorMinar]

After a long discussion we reverted this commit and decided to mark this issue as wontfix. Please see the commit message for more details.

3ea2416