Support for mpc-be

[joeoe]

As I understand it, mpc-be is practically mpc-hc only with more features and bugfixes so I assume the checker function could just accept the mpc-be exe.

[Et0h]

This suggestion has made before and last I checked MPC-BE was still missing some key API features that are present in modern versions of MPC-HC. Syncplay cannot support MPC-BE until its API has been improved.