push_frame should take frame cursor as parameter
It is a mistake when refactoring the API to use frame cursors. 9853cbdd
All functions related to stack manipulation should take a frame cursor as a parameter. Therefore,
void (*push_frame )(MuCtx *ctx, MuStackRefValue stack, MuFuncRefValue func);should be
void (*push_frame )(MuCtx *ctx, MuFCRefValue cursor, MuFuncRefValue func);