Revert "Append to existing task stores to limit writes."

Turns out I was relying on non-standard csv behaviour to cope with the duplicate
entries.  I'll refrain from naming the individual who has patched stdlib in our
deploys :/  Refs #11.

This reverts commit 6307e237a2da676ec20565b0ed683c4956e434db.
0.12.1 released.