Spent two days converting all code that deal with git-annex branch log
files to use attoparsec and bytestring builders.

For most of them, I'm not expecting much if any speed improvements, since
often git-annex only ever parses a given log file once, and writes to many
log files are only done rarely. The main candidates for speedup are chunk
logs and remote state logs. Also Group was converted to a ByteString,
which may speed up queries that involve groups. I have not benchmarked.
It was still worth doing the conversion, for consistency and better code
if not speed.

I found a few bugs in the old parsers for log files along the way.
The uuid.log parser was not preserving whitespace in repositiory
descriptions; the new one will. And the activity.log parser filtered out
unknown values, not leaving room for expansion.
