Log Message:
exim: update to 4.93.0.4.

Based on patch provided by Mike Pumford on pkgsrc-users.

Exim version 4.93+fixes
-----------------------
This is not an official release. It is just a branch, collecting
proposed bugfixes. Depending on your environment the fixes may be
necessary to build and/or run Exim successfully.

JH/05 Regard command-line receipients as tainted.

JH/07 Bug 2489: Fix crash in the "pam" expansion condition.  It seems \ 
that the
      PAM library frees one of the arguments given to it, despite the
      documentation.  Therefore a plain malloc must be used.

JH/08 Bug 2491: Use tainted buffers for the transport smtp context.  Previously
      on-stack buffers were used, resulting in a taint trap when DSN information
      copied from a received message was written into the buffer.

JH/09 Bug 2493: Harden ARC verify against Outlook, whick has been seen to mix
      the ordering of its ARC headers.  This caused a crash.

JH/10 Bug 2492: Use tainted memory for retry record when needed.  Previously when
      a new record was being constructed with information from the peer, a trap
      was taken.

JH/11 Bug 2494: Unset the default for dmarc_tld_file.  Previously a naiive
      installation would get error messages from DMARC verify, when it hit the
      nonexistent file indicated by the default.  Distros wanting DMARC enabled
      should both provide the file and set the option.
      Also enforce no DMARC verification for command-line sourced messages.

JH/12 Fix an uninitialised flag in early-pipelining.  Previously connections
      could, depending on the platform, hang at the STARTTLS response.

JH/13 Bug 2498: Reset a counter used for ARC verify before handling another
      message on a connection.  Previously if one message had ARC headers and
      the following one did not, a crash could result when adding an
      Authentication-Results: header.

JH/14 Bug 2500: Rewind some of the common-coding in string handling between the
      Exim main code and Exim-related utities.  The introduction of taint
      tracking also did many adjustments to string handling.  Since then, eximon
      frequently terminated with an assert failure.

JH/16 Fix the variables set by the gsasl authenticator.  Previously a pointer to
      library live data was being used, so the results became garbage.  Make
      copies while it is still usable.