fscks and interrupted exports, both of which will restart from the
beginning.
* Improved serialization of filenames and keys to the sqlite databases,
- avoiding encoding problems.
+ avoiding encoding problems and speeding up operations on them.
* Add some missing indexes to sqlite databases. This will speed up
some things involving export and import remotes, and git-annex smudge.
Microbenchmarks show around 10-25% speedup of sqlite database operations.