Patch to fix broken grenade prediction

[tomshackell]

I noticed the grenade prediction code was a bit buggy (in particular it really didn't work if you tried to fire at something that was below you) so I rewrote it.

The code's pretty simple but the maths is rather involved so I've included a very long comment describing how it all works, should anyone need to understand it.

The patch is to the SVN revision most current at the time of writing (revision 3845) and is available at:
 http://www-users.cs.york.ac.uk/~shackell/files/fix-grenade-trajectories.patch

thanks

Tom  

[Mattn]

i applied your patch to trunk now - thank you