rebuilt the buffered_printf code to simplify it and prevent (hopefully) the crashes that Alex Kemp finds.

added tmpstore->error_buffer to deal with errors separately,
this is handled correctly in binary_grid2 (v2.1.3+) so it
behaves just like previously and SYSTEM_ERROR is detected
correctly.

deprecated the printf_stack to remove a load of unusued code

extended the API to use the error_buffer through binary_c_error_buffer()