R1:9d474452f9c5

Make nonscalar field saves raise a more useful exception from LiskDAO

Summary:
If you do something like this:

// Missing $user->getPHID()!
$object->setUserPHID($user)->save();

...you get a very unhelpful exception:

Expected a scalar or null for %s conversion. Query: %s

This doesn't give you any hints about what's wrong. Instead, provide a more useful exception:

Unable to insert or update object of class DifferentialRevision, field 'title' has a nonscalar value.

Test Plan: {F87614}

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