FOTS: TypeswitchExpr related issues

http://www.w3.org/TR/xquery-30/#doc-xquery30-TypeswitchExpr

The following 8 test cases fail in Zorba:

test set "prod-TypeswitchExpr"
test cases : "typeswitch-union-nomatch", "typeswitch-union-nomatch-2", "typeswitch-union-branch-1", "typeswitch-union-branch-1-dup", "typeswitch-union-branch-2", "typeswitch-union-branch-2-dup", "typeswitch-union-branch-both", "typeswitch-union-branch-both-dup"

"typeswitch-union-nomatch" query:
xquery version '3.0';
declare namespace op = 'http://www.zorba-xquery.com/options/features';
declare namespace f = 'http://www.zorba-xquery.com/features';
declare option op:enable 'f:hof';
typeswitch (<e/>)
case $i as xs:integer | xs:string return $i
default $v return 0

"typeswitch-union-nomatch-2" query:
xquery version '3.0';
declare namespace op = 'http://www.zorba-xquery.com/options/features';
declare namespace f = 'http://www.zorba-xquery.com/features';
declare option op:enable 'f:hof';
typeswitch (<e/>)
case xs:integer | xs:string return 1
default $v return 0

"typeswitch-union-branch-1" query:
xquery version '3.0';
declare namespace op = 'http://www.zorba-xquery.com/options/features';
declare namespace f = 'http://www.zorba-xquery.com/features';
declare option op:enable 'f:hof';
typeswitch (47)
case $i as xs:integer | xs:string return $i
default $v return 0