ios: fix contrib compilation with Xcode 5
playlist: do not create play-and-stop variable

This was not needed (but it prevented the preferences from taking effects
until VLC was restarted).
Qt4: make exit after play sticky (refs #9612)
playlist: do create play-and-exit variable

(as with play-and-stop)
Qt: correctly play after drag and drop

Close #9502
contrib: update modplug
contrib/modplug: remove patch merged upstream