-Fix: clean up, test (somewhat), and complete the API for waiting cargo

git-svn-id: http://svn.openttd.org/trunk@26557 6aa0318a-3be1-0310-93fa-89fd2396df07
-Fix: be more explicit about the type of iterators in the waiting cargo API

git-svn-id: http://svn.openttd.org/trunk@26558 6aa0318a-3be1-0310-93fa-89fd2396df07