limit the allowed server pong rate


git-svn-id: http://svn.code.sf.net/p/sauerbraten/code@4962 07af1644-1164-4067-b897-63bf4dc9b748
limitpong fix


git-svn-id: http://svn.code.sf.net/p/sauerbraten/code@4963 07af1644-1164-4067-b897-63bf4dc9b748