In 5.0 we made LOAD DATA INFILE autocommit in all engines, while
only NDB wanted that. Users and trainers complained that it affected
InnoDB and was a change compared to 4.1 where only NDB autocommitted.
To revert to the behaviour of 4.1, we move the autocommit logic out of mysql_load() into
ha_ndbcluster::external_lock().
The result is that LOAD DATA INFILE commits all uncommitted changes
of NDB if this is an NDB table, its own changes if this is an NDB
table, but does not affect other engines.
Note: even though there is no "commit the full transaction at end"
anymore, LOAD DATA INFILE stays disabled in routines (re-entrency
problems per a comment of Pem).
Note: ha_ndbcluster::has_transactions() does not give reliable results
because it says "yes" even if transactions are disabled in this engine...