parse - a pointer to a CSPARSE structure initialized with cs_init()
funcname - the name for the CS function call
Note that registering a duplicate funcname will
raise a NERR_DUPLICATE error
str_func - a CSSTRFUNC not-callback
DESCRIPTION
cs_register_esc_strfunc functions exactly as cs_register_strfunc
except that it changes the evaluation escaping context to disable
default escaping.