Method `element_is_not_hidden` does not work as expected

[oradyvan]

The helper method element_is_not_hidden(selector) relies on sending message FEX_isVisible to given selector and then it removes all false values from the resulting array. However, due to the issue "Operations returning a BOOL broken" #27 the resulting array contains only numbers (1 or 0) so removing false does not have any effect. In the end, the failing method also affects other helper methods:

check_element_exists_and_is_visible( selector )
check_element_does_not_exist_or_is_not_visible( selector )

This particular issue can be easily fixed without fixing the issue #27. I'll try make up the fix and publish it as pull request.