Add section on allowing user access to the labelprop for a class so

that iterating over the class will work.

Ezio found this flaw in the docs while working with the python
tracker.

Mark one other section as Required. Shorten another section heading.

Author: rouilj

doc/upgrading.txt

@@ -23,6 +23,39 @@ Contents:
 Migrating from 1.5.1 to 1.6.0
 =============================
 
+Make sure that user can view labelprop on classes (REQUIRED)
+------------------------------------------------------------
+
+If you have View permissions that use ```properties=...```,
+make sure that the labelprop for the class is listed in the
+properties list.
+
+The first one of these that exists must must be in the list:
+
+ 1. the property set by a call to setlabelprop for the class
+ 2. the key of the class (as set by setkey())
+ 3. the "name" property (if it exists)
+ 4. the "title" property (if it exists)
+
+if none of those apply, you must allow
+
+ * the "id" property
+
+E.G. If your class does a setlabelprop("foo") you must include "foo"
+in the properties list even if the class has name or title properties.
+
+See:
+http://www.roundup-tracker.org/docs/customizing.html#setlabelprop-property
+for further details on the labelprop.
+
+If you don't do this, you will find that multilinks (and possibly
+links) may not be displayed properly. E.G. templates that iterate over
+a mutlilink field (with tal:repeat for example) may not show any
+content.
+
+See: https://sourceforge.net/p/roundup/mailman/message/35763294/
+for the initial discussion of the issue.
+
 Cross Site Request Forgery Detection Added
 ------------------------------------------
 
@@ -131,8 +164,8 @@ made it difficult to exploit. However allowing the use of
 subdirectories to organize the templates required that it be fixed.
 
 
-Database back end specified in config.ini
------------------------------------------
+Database back end specified in config.ini (REQUIRED)
+----------------------------------------------------
 
 The ``db/backend_name`` file is no longer used to configure the database
 backend being used for a tracker. The backend is now configured in the
@@ -371,8 +404,8 @@ change the value assigned to @dispname in the href attribute from
 ${qs/name} to ${qs/name/url_quote}. Note that you should *not* change
 the value for tal:content.
 
-Schema change to allow "Show Unassigned" issues link to work for Anonymous user
--------------------------------------------------------------------------------
+Allow "Show Unassigned" issues link to work for Anonymous user
+--------------------------------------------------------------
 
 In this release the anonymous user is allowed to search the user
 class. The following was added to the schema for all templates that