Watch for class\style expression changes only if they are defined.
Don't recalculate expression locals for isDisabled. Use one that was already calculated.
ngSelectOption  rewritten to be precalculated as others. That will allow us to use old  value in calculation of new value. + ExprLocals should not recalculate their names on each call. Names will be calculated once per ngSelectOption at the most
Merge pull request #10 from pluff/feature/optDisabled_performance

ngSelectedOption $optDisabled rewritten to be precalculated as others
merge from master