Add a pipeline to the active set only after its data has been written.

In the previous mechanism, it'd be possible for something like this to
happen:

1. SADD pipelines IDENT
2. (someone tries to examine all pipelines via SMEMBERS or SSCAN and
   finds a pipeline that doesn't exist)
3. HMSET IDENT [data]

Running HMSET first alleviates this problem.
Bump pipeline version.