docs: clarify wording, fix index, add superseder link

Make superseder, messages etc. properties index entries point to the
right place.

Link to description of using Superseder in the original overview.

fix bad wording on boolean properties.

Author: rouilj

doc/reference.txt

@@ -744,6 +744,11 @@ create(information)
 Create an item in the database. This is used to create items
 in the :term:`definitional class` like "priority" and "status".
 
+.. index:: triple: schema; class property; messages
+   triple: schema; class property; files
+   triple: schema; class property; nosy
+   triple: schema; class property; superseder
+
 IssueClass
 ~~~~~~~~~~
 
@@ -756,6 +761,8 @@ users to tell about changes to the issue. They get "CC'ed"
 e-mails when messages are sent to or generated by the issue. The nosy
 reactor (in the ``'detectors'`` directory) handles this action. The
 superseder link indicates an issue which has superseded this one.
+It is better described in the
+`original document <original_overview.html#roundupdb>`_.
 
 They also have the default "creation", "activity" and "creator"
 properties.
@@ -855,11 +862,6 @@ file class allows for other possibilities including:
   done on the filesystem outside of the Roundup mechanism.
 * keeping multiple revisions of the file.
 
-.. index:: triple: schema; class property; messages
-   triple: schema; class property; files
-   triple: schema; class property; nosy
-   triple: schema; class property; superseder
-
 .. index:: schema; item ordering
 
 A note about ordering
@@ -3084,7 +3086,7 @@ There are several methods available on these wrapper objects:
 	        Set the labels for the true/false/undefined
 		states. If u_label is defined, it produces a
 	        tri-state radio button selector. Otherwise, it
-		allows selection of true,yes/false,no only.
+		allows selection of true/yes or false/no only.
 
 	      labelfirst (Boolean properties only)
 	        place the labels before the radio buttons