Added relative or absolute argument to FileHandleResolver.resolve()

http://code.google.com/p/libgdx/issues/detail?id=1556

Made some best guesses on whether the loaders are expecting relative or absolute pathing. SkinLoader.java would be my main worry, but if there is a bug it is as simple as changing the boolean :-)

Example of an Absolute FileHandleResolver created using this setup:
```
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.assets.loaders.FileHandleResolver;
import com.badlogic.gdx.files.FileHandle;

public class AbsoluteFileHandleResolver implements FileHandleResolver {
	public AbsoluteFileHandleResolver() {
	}

	@Override
	public FileHandle resolve(String fileName, boolean relative) {
		if(relative){
			return Gdx.files.absolute(fileName);
		} else {
			return Gdx.files.absolute("C:/Users/Dave/Game/" + fileName);
		}
	}
}
```