GitLab

Fix mdb_txn_begin(&read-only txn) calls. Test mdb_env_set_maxreaders().
Rename DBI open/close functions. Move mdb_dbi_close() out of txn.

Just use srand/rand, we don't care about the quality
of the random numbers, we just want some data.

Avoid naming conflicts with other mdb* packages. Bump version to 0.9.5

mdb_close() takes an env, not a txn.
Also, add check for stale DB records (in case some other process
wrote to the DB last).