Issue Description:

when skeleton replacement is enabled, the client shows 'a fatal error has occured, connection was terminated'. server console registers a normal disconnect while the client log shows no sign of any issue.

goal of issue post: some sort of error logging for wither skeleton issues - I don't expect you to fix every possible weird mod interaction

What happens:

'a fatal error has occured, connection was terminated', no error description

What you expected to happen:

working wither skeletons or description of error, so fixing it on the other mods side (or by private bytecode mod) is possible

Steps to reproduce:

1. come as close to my modpack as possible
2. change replaceWitherSkeleton to true
3. try to connect to server
   ...

Affected Versions (Do not use "latest"):

• EnderIO: 2.3.0.492_beta
• EnderCore: 0.0.2.39_beta
• Minecraft: 1.7.10
• Forge: 7.99.40.1614

using a modified infitech 2 modpack; modlist: https://pastebin.com/Cs3aChfG

Your most recent log file where the issue was present:

irrelevant; exactly the same as normal, but you DC on first game tick

replaceWitherSkeleton is off by default and was removed in later versions for a reason...

btw ... wouldn't it be easier to add a wither bool to soul vials + powered spawners instead of replacing a vanilla entity?

does this mean you won't even add error logging? if not, please consider adding another way of making it possible to spawn wither skeletons, like flags or 'exact copy' mode.