figure out what to do about a stale writer

[mykmelez]

LMDB > Caveats notes:

A broken lockfile can cause sync issues… stale locks can block further operation. … Stale writers will be cleared automatically on some systems:

• Windows - automatic
• Linux, systems using POSIX mutexes with Robust option - automatic
• not on BSD, systems using POSIX semaphores. Otherwise just make all programs using the database close it; the lockfile is always reset on first open of the environment.

We should figure out what to do about a stale writer on systems that don't clear it automatically.