Feature request

While evaluating RobotFramework + SeleniumLibrary I found a use case where
the value of a textarea is changed and I would like to wait until the value matches some expected text.

Generally, you would expect Wait Until Element Contains would fill this scenario. But issue #167 showcases that textareas behave a little differently.

I believe that textareas would need their own Wait Until keyword to handle the .value property they contain.