treediscovery: always return all remote heads Old discovery only returned incoming heads, not all of them (for changegroupsubset). New discovery must always return all of the remote heads (for getbundle). I failed to properly adjust treediscovery in cb98fed52495 when introducing setdiscovery. The actual observable problem was 'remote: unsynced changes' when trying to push a cset on one named branch to a server with a new cset on another named branch. This scenario is now tested in test-treediscovery.t.

merge with stable