[Exim] deliver_force_thaw and logging in message_filter

We do some filtering to catch spam with our message_filter,
messages frozen are logged. The logfile is parsed to
generate some stastics etc.

Sometimes messages are unintentionally frozen,
they are forced delivered with "-M <msgid>".
However the global filter also logs the
actual delivery to the logfile of the filter.
I've seen worse problems - still it is a bit annoying.

I have found no way to avoid logging to the
filterlog when forcing a delivery and have
put this patch into production (3.12). You might
consider something similar?

Hans Morten Kind
Univ of Bergen
Norway

*** filter.c.orig       Thu Jan 27 14:02:00 2000
--- filter.c    Thu Jan 27 14:11:35 2000
***************
*** 2013,2018 ****
--- 2013,2019 ----
            }
          }
        len = (int)strlen(s);
+       if (!deliver_force_thaw) {
        if (write(log_fd, s, len) != len)
          {
          *error_pointer = string_sprintf("write error on file \"%s\": %s",
***************
*** 2020,2025 ****
--- 2021,2027 ----
          return FALSE;
          }
        }
+       }
      else
        {
        DEBUG(10) debug_printf("skipping logwrite (verifying or testing)\n");