CraftBukkit already checks that we're not trying to copy data
back to the same snapshot, reverting this fixes the ability to
properly update non-snapshot blockstates
Also adds a limit to stop sending Sign data to client after 500
signs per chunk to limit client lag.
Use -DPaper.excessiveSignsLimit=500 to configure that limit, or -1
to disable the limit and let your players be abused.
fixes#1878