This option was mainly added for people wanting to follow Mojang's recommendation to load all important world chunks in 1.6.3 - 1.6.4 before updating to the eventual 1.7 release to prevent errors with structures such as witch huts and nether fortresses:
https://mojang.com/2013/09/minecraft-snapshot-13w37a/
Working around Minecraft and Bukkit client/server glitches when teleporting an entity which has a passenger or is a passenger is the whole reason for this "feature". The need was introduced a few Minecraft versions back when this well and truly broke; hopefully they will fix the underlying problems eventually.
A delay of at least 2 ticks worked on my local VM test server, but for potentially loaded live servers on the internet with players who potentially have slow/poor connections... a longer delay is probably needed to prevent client glitches. I've set the delay to 10 ticks (half a second) which still looks reasonable enough in-game, I think.
Further, I found that out of the native vehicles boats in particular quite simply cannot be teleported without the client ending up confused about where it actually is for whatever reason. I came up with a workaround for this by destroying the boat and spawning a new one in the correct position.
Bah, gotta love workarounds within workarounds.
As a reminder, this all primarily came about due to the ability to teleport entities which have a passenger being removed by the Bukkit team to apparently combat a nasty related bug.
Players going through a portal will now no longer be able to generate chunks outside the border; the portal teleport location is re-targeted inside the border to prevent that so that new portals aren't created outside the border
added redstone comparator and activator rail to "safe open blocks" list for knockback safe location finder
Note that I tried to work around it by ejecting the player, teleporting the entity they were riding (minecart, pig, whatever), and then setting the player as passenger again, but it was bugged and only halfway treating the player as if they were riding something.
This is useful now that border shapes can be rectangular/elliptical with different X and Z radius values.
Also various cleanup of new rectangular/elliptical support. Commands can now accept a single radius value (as it used to) or separate X and Z. Radius is displayed as single number if X and Z are equal. "shape" and "wshape" commands accept round|square as before for backwards compatibility and simplicity, alongside the new elliptical|rectangular (which work the same). Updated config loader to support loading older configs with single radius value specified. Added various other methods for backwards compatibility.
New command /wb bypass [player] [on/off], which allows the player to go beyond the border without being knocked back. Requires "worldborder.bypass" permission (Ops only by default). Nobody has bypass mode enabled by default (has to be toggled on), and the list of people with bypass enabled is wiped on server restarts. Player name ("[player]") is optional if run in-game and defaults to the player running the command, but must be specified if run from console. If on or off ("[on/off]") is not specified, it will simply be toggled.
Also attempt to fix problem when riding mobs via MobRider where mob and player end up underground after knockback; seems unsuccessful. Seeing as pigs in vanilla CraftBukkit without MobRider don't have this problem, but _do_ have the problem along with all other mobs when MobRider is loaded, I'm not bothering with this one further for now.
Also added variables for Dynmap border color/thickness/opacity, just for internal clarity... will also simplify things if I or someone else ever gets around to adding settings for those values, to allow them to be changed
