output MDL-20327 Made moodle_core_renderer::link set a target attribute if CFG->frametarget is not empty
 This only occurs if the administrator sets the frame name setting for Moodle to something other than default _top
or if frametarget has been overriden manually

 * If no active node is found when the navigation is called upon then we attempt to find a best match active node
 * Links are now produced with frame breakout actions
 * Links ending with / are presumed index.php for matching purposes

As Petr suggested, is_array() is faster than empty() so it makes sense
to check it first.

apply correct $default_for_char, so each DB will get its correct empty value

work with all CHAR/CLOB columns and implemente oracle transactions support.