A number of worlds use leaves as the basis for sculptures. If the
sculptures are destroyed by leaf decay, turning leaf decay off
won't restore them.
However, for worlds where the host wants to use leaf decay, there
are no negative consequences to having leaf decay off initially
and then turning it on.
So, leaf decay has been turned off by default.
As part of this, the parameter "disable_leaf_decay" has been re-
placed with "enable_leaf_decay". The default setting for the new
enable_leaf_decay = false