Add commented mutexes on data cache
Add commented mutexes on data cache

There needs to be a mutex *somewhere* around these maps. These are there
as a warning reminder that something needs to be done, even though a
per-map mutex system seems very unlikely to have sufficient performance
benefit to offset the complexity cost (and concomitant deadlock risk).

golang/dep,ibrasho-forks/dep,ibrasho-forks/dep,golang/dep,golang/dep