fix bug in 'CASE' statement, now also the ELSE part gets properly converted to the supertype.
fix bug in 'CASE' statement, now also the ELSE part gets properly converted
to the supertype.

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb