Pull request for authors listing feature improvments

[Guilhem Bonnefille <guilhem bonnefille gmail com>]

Hi,

Please, consider to merge (or chery-pick) my work on the following branch:
https://github.com/guyou/giggle/tree/improve-authors-listing

First commit add a test: useful before modifing code.

Next commit improve listing performance: lest data writen, less data read.

Final commit allows to request authors of current branch or all
branches. This feature is not yet used in UI, but I'm working on this
topic. Will be available later.


Thanks in advance for maintaining this tool.
-- 
Guilhem BONNEFILLE
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