obscache: distinct 'clear' and 'reset' We make a difference between basic invalidatiton (or lack of loading) and 'reset' (current cache data are invalid). We can now ensure a non-None key when we start the update. This will allow us to "update" the existing key instead of recomputing one from scratch. This is more efficient and less racy.

merge with stable

serveronly: also enable the obscache for server only setting The obscache is useful and speeds things up. So we also enable for server only setting.