make pdfview first responder on mouse down, because 10.6 doesn't do that automatically anymore
make pdfview first responder on mouse down, because 10.6 doesn't do that automatically anymore

git-svn-id: 765db44a9620ed55f4f8addfd3c14fe8cd57f6bb@5650 0fceea05-a30d-0410-8a8b-80ef821fb0a1

nanoant/Skim,nanoant/Skim,nanoant/Skim,nanoant/Skim,nanoant/Skim