Add automatic handling of MoveTargetOutOfBounds exceptions

MoveTargetOutOfBounds exceptions are sometimes thrown instead of
ElementNotVisible exceptions. This can happen when the Selenium2 driver
for Mink moves the cursor on an element using the "moveto" method of the
Webdriver session, for example, before clicking on an element. In that
case, if the element is not visible, "moveto" would throw a
MoveTargetOutOfBounds exception instead of an ElementNotVisible
exception, so those cases are handled like ElementNotVisible exceptions.

Note that MoveTargetOutOfBounds exceptions could be thrown too if the
element was visible but "out of reach"; there is no problem in handling
those cases as if the element was not visible, as the exception will be
thrown again anyway once it is verified that the element is indeed
visible.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>