code: @SuppressWarnings("unchecked")
      public int diffSchema(DiffSet diffSet, DifferenceReporter reporter) {
  
          CountingReporter countingReporter = new CountingReporter(reporter);
          diffSchemaImpl(diffSet, countingReporter);
          return countingReporter.breakingCount;
      }
docs: This will perform a difference on the two schemas.  The reporter callback
  interface will be called when differences are encountered.
  
  @param diffSet  the two schemas to compare for difference
  @param reporter the place to report difference events to
  
  @return the number of API breaking changes