log gatherer should auto-rotate+compress logfiles

[Brian Warner]

The log gatherer process should periodically close, compress, rename, and reopen its generated logfiles. These files should acquire a name derived from the starting and ending timestamps, and be bz2-compressed. I'm thinking they should be rotated every 24 hours, and also in response to SIGHUP.

This would make the gatherer a lot more usable. At the moment, it emits everything to a very large non-compressed pickle file, which grows so big that it becomes impossible to work with. Rotating the file is a hazardous operation: it is easy to accidentally delete it (since the gatherer truncates an existing file), and the gatherer will lose events while it is offline.

[Brian Warner]

Fixed, in [976383c7985a63e4eca2fb3ed28054596f00820e]