Column mismatch for concat crashes

This crashes

 view {a b} def {1 2 3 4} | concat [view a def {1 2 3 4}] | dump

and so does this

 view {a b} def {1 2 3 4} | union [view a def {1 2 3 4}] | dump

Summary

Thanks, I've added some tests to prevent a crash for concat, union, and intersect (and probably a few more operators depending on them). The error code is unfortunately not very clear: invalid view. But it's not easy to change that at the level of code where this happens.

Changes committed to svn.