[MERGE][0.91] Make RemoteRepository.sprout cope gracefully with servers that don't support the 'Repository.tarball' request.

[Bundle Buggy]

Bundle Buggy has detected this merge request.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C20070914031103.GA32195%40steerpike.home.puzzling.org%3E