and checks if all values are actually defined are done in one
file now (and not in two different classes as before). Added
doxygen comments as well.
2) More physics improvements.
git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/trunk/supertuxkart@2345 178a84e3-b1eb-0310-8ba1-8eac791a3b58