[SDL] Adding SpaceNavigator support to libSDL

[Ettore Pasquini]

I made a patch for adding support to the SpaceNavigator and other 3Dconnexion devices on Linux:

http://cubelogic.org/dev/libsdl/20080428/spacenav-libsdl1.3.patch

To apply, cd into your trunk working copy and give a 
$ patch -p0 < spacenav-libsdl1.3.patch

I tested it against the SDLJoytest-GL sample code and it seems to work seamlessly. Basically the new (relative) event devices are recognized as a possible choice. 

I think my changes are fairly straightforward but please feel free to ask any questions or give any feedback, especially if there's something missing or wrong.  My objective of course would be to see this merged into the trunk.

Ettore