Check for specific keys in db config to recognize missing config
Check for specific keys in db config to recognize missing config

Sometimes stuff (eg. search path) is set from elsewhere. But a config
with no adapter nor url is unlikely to be valid.

Note this is purely cosmetic change: it would fail either way, but
this allows for a better error message.

TalentBox/sequel-rails,jarredholman/sequel-rails,zBMNForks/sequel-rails,zBMNForks/sequel-rails,amaniak/sequel-rails,jarredholman/sequel-rails,amaniak/sequel-rails,TalentBox/sequel-rails