[MBS] OverlayMBS closed in thread : don't do it

Just ran into a baffling bug with OverlayMBS - turned out I was closing them inside a thread. Although everything looked normal, this was causing many problems later on including an eventual crash. It was extremely hard to debug this, as you can imagine. Christian - I wonder if you could add

[MBS] [ANN] 5.3pr1

Hi, * Rewrote PHP plugin part to use PHP version 5.6.12 and work with 64-bit. * Added new 64-bit plugin for Mac covering Accounts, Social and EventKit classes. * Added gamma option to QTPictureMovieTrackMBS class * Updated SQLite to 3.8.11. * Fixed ChartDirector license check for 64-bit. * Fixed