fixed bugs in ifthenelse (return a proper nil value) and cast (don't free old value (is done by the interpreter))
fixed bugs in ifthenelse (return a proper nil value) and cast (don't free
old value (is done by the interpreter))

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