1.8.6 Sign Crash

When you guys fixed signs you removed the server-side check that limits the length of a line. Only two people noticed this but they are abusing servers left and right (crashes clients who render the chunks and lags the server). Clever json can make it run out of memory.

Please do NOT give me credit for disclosing this. I was told about this confidentially and won't be able to pass on more if you do.