Issue: Registration of UCI engines to play variants

[Johannes Czech]

Dear XBoard-Developers,

thank you for awesome work in creating an open-source cross platform chess variant GUI.

I tried setting up the UCI-chess variant engine Multi-Variant-Stockfish (https://github.com/ddugovic/Stockfish)
and the neural network engine CrazyAra (https://github.com/QueensGambit/CrazyAra) using the python version in XBoard to play crazyhouse.

However, I encountered the following error messages for both of them:
"Error: Variant crazyhouse not supported by <engine-name>"
although both them actually support the variant.

This is the configuration that I chose: Engine->Edit Engine List...
"stockfish-x86_64-modern" -fcp "/home/queensgambit/Programs/cz_engines/stockfish/stockfish-x86_64-modern" -fd "/home/queensgambit/Programs/cz_engines/stockfish" -fUCI
"CrazyAra-0.5.1" -fcp "/home/queensgambit/anaconda3/bin/python crazyara.py" -fd "/home/queensgambit/Desktop/CrazyAra_0.5.1_RiseV2_mobile" -fn "CrazyAra-0.5.1" -fUCI -variant crazyhouse

After I added
-firstProtocolVersion 1
to the configuration of CrazyAra, I didn't encounter the error, but CrazyAra exited after the first move.

Did I miss a certain setting or could this be a bug in XBoard?

More details can also be found at:
* https://github.com/QueensGambit/CrazyAra/issues/23


Best regards,
Johannes Czech