Bugs already present in the original game

[Lectem]

The original game as a lot of bugs, and we need to decide what to do about it.
Since D2MOO's main objective is to implement the vanilla game, we must keep the code of those bugs, and document them.
We could probably still fix them, and use a macro for such code to enable/disable fixes.

I'm adding a new Label for bugs reported that might have an impact to modders, but were already present in the original game, thus not due to D2MOO.

Such bugs must be both labeled and reference this issue.

[Lectem]

For the bugs we fix, put them behind a NO_BUG_FIX macro check that allows to obtain vanilla behavior.