IncompatibleChanges out, README.UPDATING updated.

I forgot about README.UPDATING and introduced a new txt file with the
4.73 release, noting incompatible changes. Because these weren't
documented in the normal place, some people missed them. Mea culpa.

Integrated the notes from IncompatibleChanges into README.UPDATING.

Added a note on the ABI of the dynlookups.

1 files changed, 46 insertions, 0 deletions

diff --git a/src/README.UPDATING b/src/README.UPDATING
index e81f01c13..40210a800 100644
--- a/src/README.UPDATING
+++ b/src/README.UPDATING
@@ -27,6 +27,52 @@ there have been two big upheavals...
 The rest of this document contains information about changes in 4.xx releases
 that might affect a running system.
 
+
+Exim version 4.74
+-----------------
+
+ * No incompatible changes within Exim itself, but the integrated support for
+   dynamically loadable lookup modules has an ABI change from the modules
+   supported by some OS vendors through an unofficial patch. Don't try to
+   mix & match.
+
+
+Exim version 4.73
+-----------------
+
+ * The Exim run-time user can no longer be root; this was always
+   strongly discouraged, but is now prohibited both at build and
+   run-time.  If you need Exim to run routinely as root, you'll need to
+   patch the source and accept the risk.  Here be dragons.
+
+ * Exim will no longer accept a configuration file owned by the Exim
+   run-time user, unless that account is explicitly the value in
+   CONFIGURE_OWNER, which we discourage.  Exim now checks to ensure that
+   files are not writable by other accounts.
+
+ * The ALT_CONFIG_ROOT_ONLY build option is no longer optional and is forced
+   on; the Exim user can, by default, no longer use -C/-D and retain privilege.
+   Two new build options mitigate this.
+
+    * TRUSTED_CONFIG_LIST defines a file containing a whitelist of config
+      files that are trusted to be selected by the Exim user; one per line.
+      This is the recommended approach going forward.
+
+    * WHITELIST_D_MACROS defines a colon-separated list of macro names which
+      the Exim run-time user may safely pass without dropping privileges.
+      Because changes to this involve a recompile, this is not the recommended
+      approach but may ease transition.  The values of the macros, when
+      overriden, are constrained to match this regex: ^[A-Za-z0-9_/.-]*$
+
+ * The system_filter_user option now defaults to the Exim run-time user,
+   rather than root.  You can still set it explicitly to root and this
+   can be done with prior versions too, letting you roll versions
+   without needing to change this configuration option.
+
+ * ClamAV must be at least version 0.95 unless WITH_OLD_CLAMAV_STREAM is
+   defined at build time.
+
+
 Exim version 4.70
 -----------------