column_property() should raise an exception if given expression does not have a name

[Mike Bayer]

in ExternalColumnsTest, removing the label()s from each expression causes the mapper to not recognize the columns when they come back in the result set. should fail up at configuration time with a descriptive message.

[Mike Bayer]

jbellis fixes this in changeset:3039

[Mike Bayer]

Removing milestone: 0.4.0 (automated comment)