FlxPoint support for log and watch

`FlxPoints` are usually some of the more common things you use when debugging via `log` and `watch` - unfortunately, all you would get when doing that is the class name (`FlxPoint`). 

With this commit,
```
FlxG.watch(sprite, "velocity", "Sprite velocity"); 
FlxG.watch(sprite, "_point", "Sprite position");
```
and `FlxG.log(sprite._point);` in `update()` [look like this](http://i.imgur.com/NerOc3V.png).

Unfortunately, for `log` this only works when you only pass the point only without additional text. So `FlxG.log("Velocity is now " + sprite.velocity);` - that'll still get you `"Velocity is now: FlxPoint"`. I don't think there's a way to make that work without changing the way `log` works substantially (several params?) as the `Data` passed will always be a String in this case.

I decided to round the points to integers. Everything else just doesn't seem very readable / convenient. If you need more precision, you can still use the more laborious approach of watching `point.x` and `point.x` separately / calling.

Another thing is that the text displayed in the `WatchEntry` is obviously not a valid value for a `FlxPoint`, so clicking that and clicking elsewhere will cause a crash. I believe [this recent commit](https://github.com/Beeblerox/HaxeFlixel/commit/d3b738f504ad57bebbbb6e373092662a58ad4e8c) on the texture_atlas branch should fix this though.