Coxpcall encapsulates the protected calls with a coroutine based loop, so
errors can be handled without the usual pcall/xpcall issues with coroutines
for Lua 5.1.

Lua 5.2 was extended with the Coxpcall functionality and hence it is no
longer required. The 5.2+ compatibility by coxpcall means that it maintains
backward compatibility while using the built-in Lua implementation.