Drag interval of 0 (i.e. no separate cycle) seems appropriate now

The reason for setting this to 1 was ancient IPhones with ancient iOS
versions. On all other devices, 0 seems to work better, and it removes the
overhead of spawning a separate cycle for each drag.
Merge pull request #991 from ahocevar/drag-interval

Kinetic dragging causes multiple requests and hangs an application. r=@bartvde