Spot nested columns in query conditions and report an ad-hoc error.
Spot nested columns in query conditions and report an ad-hoc error.

Nested columns are allowed by `Table._extendedWithDefVars()` as is instead of
converted to an array, so that `_getConditionKey()` is able to spot them and
report a nice error instead of just complaining about an object data type.


git-svn-id: 92c705c98a17f0f7623a131b3c42ed50fcde59b4@1854 1b98710c-d8ec-0310-ae81-f5f2bcd8cb94

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