Merge branch 'master' into topic/constructor_rewrite

Merge branch 'master' into topic/constructor_rewrite

Add some extra code to enforce the assumption that any bind type constant
is accessible in _dbi_attrs_for_bind, or in other words that all necessary
DBDs are already loaded (concept originally introduced in ad7c50fc)

Without this the combination of 9930caaf7e (do not recalculate bind attrs
on dbh_do retry) and a2f228547 (do not wrap iterators in dbh_do) can result
in _dbi_attrs_for_bind being called before DBI/DBD::* has been loaded at all