Harden retrieving recurrence objects if calendar is busy
Harden retrieving recurrence objects if calendar is busy

Try ten times, before bailing out.
Fixes bug 580724.

matzipan/evolution-data-server,gcampax/evolution-data-server,tintou/evolution-data-server,matzipan/evolution-data-server,gcampax/evolution-data-server,matzipan/evolution-data-server,matzipan/evolution-data-server,gcampax/evolution-data-server,tintou/evolution-data-server,Distrotech/evolution-data-server,tintou/evolution-data-server,Distrotech/evolution-data-server,matzipan/evolution-data-server,tintou/evolution-data-server,Distrotech/evolution-data-server,Distrotech/evolution-data-server,gcampax/evolution-data-server,Distrotech/evolution-data-server