Added Round functions to Vector2 to complement the Truncate and Ceiling methods for converting a Vector2F.

Added reverse scalar multiplication vector operators to allow either ordering.
Fixed bug in Main where filter would be out of sync with display after reloading from editor. Filter will now be reset too to ensure consistency.
Fixed some disposal checks in AnimationLoopBase to ensure they run after disposal and not during disposal - so the animation thread can first shut down.
Fixed some errors regarding interaction setup and activation.

- Setup would intersect with all ponies rather than just targets, effectively eliminating interactions in many cases.
- Activation would exclude busy targets when checking, but not activating, it now does this.
- The current instance is removed from being a candidate target (for ponies that interact with copies of themselves).
Changed MacOSX native methods back to using GC.KeepAlive instead of HandleRef. A recent bug report suggests some native memory was freed when trying to send the selector to the window. Just guessing really.
Tweaked PonyShutdown to show MainForm when an unspecified ExitRequest is returned from the animator.
Changed mouseover checks in Pony to go through a consistent method. Also cache the behavior to make checking for the cursor being over the required region cheaper.
Drop the frame rate from 30 to 25 as images are animated with durations of 40ms or more per frame (97%). So for most images there is no need to update more often than this. This should reduce CPU load a touch.