Pkey and multichannel expansion kills server

[jamshark70]

@scztt

This would detect recursion and throw when you were using the debug event type.

The approach in these two posts also detects circular references:

• Order of execution - #12 by jamshark70
• Order of execution - #13 by jamshark70

(Though it does break one uncommon usage, noted a bit later in that thread.)

hjh