Fixed a problem with boostbook printing an extra colon in the class

synopsis, when a class inherits from a single base class and it's too 
long to fit on one line.


[SVN r40048]

tools/boostbook

@@ -1 +1 @@
-Subproject commit caeaebade43599f91ecaa2f32e5454144487f54c
+Subproject commit ebff982ef1b779032345ac2c544034feea91078d