Minecraft wiki entry for Development_versions, associated text: The /clone command now copies signal strength for Levers and Redstone Dust.
The /structure command can now specify a <to: x y z> position argument with y below 0 as long as it is equal or above the minimum height for that dimension.
Added functionality for Intellisense options: "d" and "default" in the gamemode command selector.
Minecart with Command Block can now use the self selector (@s) in its commands to target itself.
The /time set command now sets the correct time and day when specifying a time above 24000 or below the current time (e.g. /time set 0 sets the day to 0, /time set 28000 sets the day to 1), and /time can now set or add to a negative world time.