issue2551232 - modify in-reply-to threading when multiple matches if an email is missing an issue designator, in-reply-to threading is attempted. In this change if in-reply-to threading matches multiple issues, fall back to matching on subject. It used to just arbitrairly choose the first matching issue.

#!/usr/bin/env python3
import sys
import roundup

from roundup.demo import main

sys.exit(main())