(Touch) Ensure leave events are emitted to an actor that's detatched then re-attached...

(Touch) Ensure leave events are emitted to an actor that's detatched then re-attached to the stage in quick succession

[problem]      The primary hit actor is removed from the stage then re-added between motion events.
[cause]        Problem is that when it is removed, we have a flag to say we have disconnected
               from it. Normally we set a different actor on the next touch but if we set the same
               actor again, then this flag is not reset.
[solution]     Reset the flag when setting the actor.

Change-Id: Ia64fe0ac91107ada391f91a7d7b3d5a7a1280e84
Signed-off-by: Adeel Kazmi <adeel.kazmi@samsung.com>