value data: fix for clear value data for multilingual properties

git-svn-id: http://svn.flexive.org/repository/flexive/trunk@2939 d35d4baa-7912-0410-b0ae-edacad209e15
value data: added equals check for value data

git-svn-id: http://svn.flexive.org/repository/flexive/trunk@2940 d35d4baa-7912-0410-b0ae-edacad209e15
value data: null check for equals check for value data

git-svn-id: http://svn.flexive.org/repository/flexive/trunk@2941 d35d4baa-7912-0410-b0ae-edacad209e15