Bug 632670 - Chain-on-update logs managed-entries-plugin errors

When using chain-on-update, SLAPI_ENTRY_POST_OP will not be set on
the consumer for a post-modify callback.  The managed entry plug-in
currently logs a fatal message if it is unable to fetch the post-op
entry.

This patch simply changes the message to the SLAPI_LOG_PLUGIN
level.  This is fine as we have no work to do if we do not have a
post-op entry.

ldap/servers/plugins/mep/mep.c

@@ -1902,10 +1902,11 @@ mep_mod_post_op(Slapi_PBlock *pb)
             goto bail;
         }
 
-        /* Fetch the modified entry. */
+        /* Fetch the modified entry.  This will not be set for a chaining
+	 * backend, so don't treat the message as fatal. */
         slapi_pblock_get(pb, SLAPI_ENTRY_POST_OP, &e);
         if (e == NULL) {
-            slapi_log_error(SLAPI_LOG_FATAL, MEP_PLUGIN_SUBSYSTEM,
+            slapi_log_error(SLAPI_LOG_PLUGIN, MEP_PLUGIN_SUBSYSTEM,
                             "mep_mod_post_op: Unable to fetch postop entry.\n");
             goto bail;
         }