Include tests for type='last'. Improve coverage.
Include tests for type='last'. Improve coverage.

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