Function to write to error log

The need is for a function that writes to the error log (stderr on Linux). This is useful for example when debugging application code in general, but in particular stored procedure code.

SQL Function
ERROR_LOG(string)
Return value
INTEGER - 0 if the write is successful, else 1, for example if the function is not enabled.
Variable
user_log_to_error_log - Boolean setting that controls if the writes to the error log from a user is allowed. If not enabled, the function can still be called but will return 1.
Privileges
A user needs FILE privilege for the function to write data to the error log. If a user lacks FILE privilege that function returns 1