AnnexRead has recently been split out of AnnexState,
and reading values from it is faster (no MVar). So,
anything that never needs to be modified while git-annex is running can be
moved to AnnexRead for a performance win and also to make clean how it's
used. --[[Joey]]

> [[done]]; all AnnexState fields have been checked and all that can be
> made readonly are. --[[Joey]]
