[#4691] Prevent needless walks up the commit tree when computing LCDs

Signed-off-by: Cory Johns <johnsca@geek.net>
[#4691] Work-around for old, incorrectly computed DiffInfoDocs

Signed-off-by: Cory Johns <johnsca@geek.net>
[#4691] Changed refresh-last-commits.py to mark repo as analyzing and post refresh for new commits when done

Signed-off-by: Cory Johns <johnsca@geek.net>