Before we mmap(2) file for reading, and use a buffer to handle CGI scripts. Turns out, for sequential access over the whole mmap isn't better than our loop on read. This has also the additional advantage that we can use handle_cgi (now handle_copy) for both files and CGI, which is pretty cool. This also fixes a nasty bug where we could hang a connection forever, because we scheduled the wrong type of event (read on POLLOUT and write on POLLIN, it's the other way around!)

now it's symmetrical to listener_main().

keep mark_nonblock in utils.c, as otherwise the build for the regress suite will fail (mark_nonblock needs fatal which is in gmid.c, and we can't link gmid.o with the regress suite...)