Cleaned drop handling code a bit more in NSTableView

git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/gui/trunk@36170 72102866-910b-0410-8b05-ffd578937521
Fixed typo in comment

git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/gui/trunk@36171 72102866-910b-0410-8b05-ffd578937521