'Print a summary of errors by category, and the total.'

def PrintErrorCounts(self):

    for (category, count) in self.errors_by_category.iteritems():
        sys.stderr.write(("Category    '%s'    errors    found:    %d\n" % (category, count)))
    sys.stderr.write(('Total    errors    found:    %d\n' % self.error_count))
