-renamed ViewPort to Camera

-renamed ViewPort to Camera
-removed type() function from GameObject, you should better use C++ RTTI:
  * casting: BadGuy* badguy = dynamic_cast<BadGuy*> (object);
  * comparing for specific type if(typeid(object) == typeid(BadGuy))
  * getting the name typeid(object).name()
-moved camera handling into Camera class
-tweaked camera behaviour. Look for details in
  http://netpanzer.berlios.de/supertux/index.php/Camera
 Horizontal scrolling seems to be nicely now, vertical scrolling is still a bit
 too hectically...

SVN-Revision: 1309