Not to warn about secondary plugin type if standard format is used in both of primary and secondary

[ganmacs]

Now, Fluentd shows warning if secondary plugin type is different from primary plugin type. But it is nonsense in some cases in Fluentd v0.14. This propose to suppress it if both of primary and secondary use "standard" format, instead of implementing format method by themselves.

Fluentd v0.12 requires buffered output plugins to implement format method by themselves. It means that different plugin types have different formatting of buffer chunks.
Secondary plugin uses buffer chunks formatted by primary plugins. So different plugin types between primary and secondary should causes unexpected errors or failures to operate buffer chunks.

But Fluentd v0.14 has "standard" format, so different plugin types can share the way to format buffer chunks by using standard format.
There is no need to warn about type difference between primary and secondary if both these use standard format.
It can be implemented by checking plugins implement format method by themselves or not.