Emit a warning when using `mariadb-dump --gtid` on versions without GTIDs

如题。
GTID is no such thing to dump on servers that don't support GTID.

Perhaps even abort the program early in error unless --force is given.
It appears that the current behaviour (regardless of --dump-slave) on dumping GTID-less servers already skips generating SQL statements for GTIDs, albeit still outputting those statements' description comments.
(An aside: This should probably be improved.)

"versions without GTIDs" are

• MariaDB before 10.0 (long EOL - not supported by 13.0.1's mariadb-dump)
• MySQL, which has a different and incompatible implementation of "GTIDs".