dropCheck argument

give dropCheck the draggable element as promised.
Merge remote-tracking branch 'spenthil/master' into drop-improvements
Pass pointer event to getDropEvents

Fixes a bug in Firefox
Merge branch 'drop-improvements'

Fixes errors introduced by the drop refactor.
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Pass pointer event to getDropEvents
  dropCheck argument

Conflicts:
	interact.js