Tell the YUI drag/drop delegate that the show/hide and dock icons are not valid drag handles. Otherwise, a drag can be initiated by showing or hiding a block (probably not from docking one, but better safe than sorry). Not strictly related to MDL-34328, but likely to be encountered whilst testing - and closely related to another patch for MDL-34328.
Note that the "invalid" config option for the delegate takes a string - not an array - but can have multiple selectors separated by commas.
This fix checks that the empty block region is actaually the standard one, so
it can be hidden. The blocks move operating area is not resticted to page
content any more.
Paul Nicholls