Overwrite Issues

[skeenp]

Currently, you need to explicitly set overwrite to false if you want to append. Not a major problem but worth checking. I've provided a branch with one fix, maintining the overwrite variables value but bypassing overwrite if append or add fields is requested. Alternativly, the overwrite variable could be set to false if append of add fields is requested, or an update of the documentation about the behaviour could also work.