Add stderr options for gbprint output

[gilburns]

Please add the option to output to stderr.

Something like:

void gbprinterr(NSString *format, ...) { va_list arguments; va_start(arguments, format); gb_printf_worker(stderr, format, arguments); va_end(arguments); }

void gbprinterrln(NSString *format, ...) { va_list arguments; va_start(arguments, format); format = [format stringByAppendingString:@"\n"]; gb_printf_worker(stderr, format, arguments); va_end(arguments); }