CRM-8075 contributions deleted when modifying overdue pledge

Symptoms like CRM-8075

Data set up is an overdue pledge with pledge payments being a mixture of completed & pending. If you then go to edit that pledge the existing payments & contributions are deleted.

This is mitigated by the fact that data should not be in that state - I did replicate getting it into that state in 4.5 through the UI but couldn't re-replicate. On real sites it is likely that the use of the api helps to get into this state.

@joemurray - the flow is that when a 'overdue' pledge is edited ALL pledge payments are deleted. The flow on from this is that the contributions are deleted by the FK.

I think this

https://github.com/civicrm/civicrm-core/blob/master/CRM/Pledge/BAO/PledgePayment.php#L278

should go. I'm not even sure we should delete pending contributions - thoughts?

Further I don't think the deleting & recreating of the pledge_payments makes sense - I guess if was a quick code solution at the time.