Open column groups with the default overwrite configuration, true.
A simpler solution, avoiding the additional search of the primary cursor,
clear/restore the overwrite flag before/after the initial insert, and use
the error from the primary insert call as before.
Merge branch 'develop' into column-group-overwrite-config
Use a blind insert in the primary of tables with no indices.
refs #667
Merge pull request #667 from wiredtiger/column-group-overwrite-config

Have table cursors do blind updates on column groups where possible.