This extension produces quite a lot of informational messages during
its normal operation and it is hard to say which strings can be
changed and which cannot.
The leading space in the written file makes sure that the feature list never
can match an existing version, even if the first feature can be read as hex.
Additionally old hg versions display the id with --debug, too.
- if no patches are applied, don't do anything different
- if the cache includes valid data from one of the patch revisions,
use the cache, but don't save anything new
- if the cache has data from before the patch revisions only,
save what the list of branches would be without the patch revisions