Signs (bug found and feature request?)

[xoft]

The signs are behaving really weird. It almost seems like the client doesn't send the correct packet - it really sends a "-1" as the item currently held, which MCServer disallows because the server knows that the client's player is holding a sign.

I could theoretically make a check that this special case is allowed, but I don't quite like it - there still has to be something else going on here.