Fix for Trac #497: allow bulk modification of "duration" fields.

- Proper display of the modifications on the SynchroAttributes in the History of a SynchroDataSource
- Better display of the history of Boolean atrtibutes (false is no longer displayed as an empty string)

SVN:trunk[2478]

core/attributedef.class.inc.php

@@ -1263,6 +1263,10 @@ class AttributeBoolean extends AttributeInteger
 	{
 		return $sValue ? '1' : '0';
 	}
+	public function GetAsHTML($sValue, $oHostObject = null, $bLocalize = true)
+	{
+		return $sValue ? '1' : '0';
+	}
 }
 
 /**