Update to 1.642

Upstream changes:
Changes in DBI 1.642 - 28th October 2018

Fix '.' in @INC for proxy test under parallel load
    thanks to H.Merijn Brand.
Fix driver-related croak() in DBI->connect to report the original DSN
    thanks to maxatome #67

Introduce a new statement DBI method $sth->last_insert_id()
    thanks to pali #64
Allow to call $dbh->last_insert_id() method without arguments
    thanks to pali #64
Added a new XS API function variant dbd_db_do6()
    thanks to Pali #61

Fix misprints in doc of selectall_hashref
    thanks to Perlover #69
Remove outdated links to DBI related training resources. RT#125999

(wen)