Fix the _process_dist_git method so it actually updates PDC
The pdc-updater code that we rely upon here had basically three methods.
One was to react on a specific message, one was to audit the PDC vs the
source of info and the third one was to go through the entire source of
info and update PDC accordingly.
In the port of this code to toddler the methods 2 and 3 were inverted.
In toddlers we do not really care about the method #2 but we do about
method #3 which allows to periodically check that everything is in sync.
So this commit changes the _process_dist_git method to ensure that it
actually updates PDC based on the information it finds on dist-git.
Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>