Subsequent fetches can use these for negotiation and only download new
objects instead of downloading the entire history.
The tests are changed to mostly ignore all synthetic refs, since
changing evrey test would be a nightmare. But a few tests have to
care about synthetic refs because they are directly testing synthetic
refs. Fortunately, there are no cases of tests that care about
some but not all such refs.
Subsequent fetches can use these for negotiation and only download new objects instead of downloading the entire history.
The tests are changed to mostly ignore all synthetic refs, since changing evrey test would be a nightmare. But a few tests have to care about synthetic refs because they are directly testing synthetic refs. Fortunately, there are no cases of tests that care about some but not all such refs.