Polish allow unlimitted sessions

Update the rnc file

Issue gh-3900

config/src/main/resources/org/springframework/security/config/spring-security-4.2.rnc

@@ -545,8 +545,8 @@ concurrency-control =
 	element concurrency-control {concurrency-control.attlist, empty}
 
 concurrency-control.attlist &=
-	## The maximum number of sessions a single authenticated user can have open at the same time. Defaults to "1".
-	attribute max-sessions {xsd:positiveInteger}?
+	## The maximum number of sessions a single authenticated user can have open at the same time. Defaults to "1". A negative value denotes unlimitted sessions.
+	attribute max-sessions {xsd:integer}?
 concurrency-control.attlist &=
 	## The URL a user will be redirected to if they attempt to use a session which has been "expired" because they have logged in again.
 	attribute expired-url {xsd:token}?

config/src/main/resources/org/springframework/security/config/spring-security-4.2.xsd

@@ -1756,7 +1756,7 @@
       <xs:attribute name="max-sessions" type="xs:integer">
          <xs:annotation>
             <xs:documentation>The maximum number of sessions a single authenticated user can have open at the same time.
-                Defaults to "1".
+                Defaults to "1". A negative value denotes unlimitted sessions.
                 </xs:documentation>
          </xs:annotation>
       </xs:attribute>