1) Added bullet collision handling, e.g. rocket hits are now
detected by bullet code, bombs will be passed on etc.
2) Rockets are now handled by bullet as well.
3) Moved expected location of bullet from STK/bullet to
STK/src/bullet.
git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/trunk/supertuxkart@1280 178a84e3-b1eb-0310-8ba1-8eac791a3b58