Log Message:
Update py-whisper to 0.9.12.

Changes in 0.9.12:
- Just a version bump.

Changes in 0.9.11:
- Better commandline sanity checking and messaging (sejeff)
- Handle SIGPIPE correctly in commandline utils (sejeff)
- Option to intelligently aggregate values on whisper-resize (jens-rantil)
- Use more efficient max() instead of sorted()[-1] (ryepup)
- Add fallocate() support (slackhappy)
- Improve handling of exceptional fetch cases (dieterbe)
- Improve rrd2whisper's handling of rrd files
- Improve error messaging on retention errors at create time (lambdafu)
- Python2.4 compatibility for whisper-dump.py (snore)
- Correct filtering of duplicate values to ensure last-write-wins