Long initial indexing may lead to repository starvation

When FishEye detects number of repositories that need to be indexed (number of repositories added around the same time, or instance being migrated to another box with no FishEye caches), each Initial Pinger thread may spend a long time (hours, days) indexing particular repository. That leads to starvation of other repositories.

Although in the short term it seems sensible to keep Initial Pinger threads "sticky", to avoid context switching, perhaps FishEye could ignore this "stickiness" after some threshold (e.g. 1h) so other repositories would have a chance to get indexed too.