The function to override.
The function arguments, as a coma separated string.
Usually you will want to pass this parameter, as well as the
function_code parameter, as a single quote
delimited string. The reason for using single quoted strings, is to
protect the variable names from parsing, otherwise, if you use double
quotes there will be a need to escape the variable names, e.g.
The new code for the function.
override_function('test', '$a,$b', 'echo "DOING TEST"; return $a * $b;');