Fix memory leaks thro' valgrind in 'melt'.
Fix memory leaks thro' valgrind in 'melt'.

Rdatatable/data.table,vlulla/data.table,jangorecki/data.table,jangorecki/data.table,vlulla/data.table,jangorecki/data.table,vlulla/data.table,jangorecki/data.table,Rdatatable/data.table,Rdatatable/data.table,vlulla/data.table,Rdatatable/data.table