UploadWithTracker: Don't fail but retry if tracker URI is bad.

(cherry picked from commit c55e24ca06da3be2282967d611f6cf950474fb24)
UploadWithTracker: Require match trailing slash for all URIs.

Re: ArchiveTeam/seesaw-kit#60

(cherry picked from commit 876fc8eefe07dde57fa933d6e4aa810f55643e4c)