Merge destroys custom data linked to contact_sub_type without warning user

Two contacts, A and B.

A: Individual, no custom data
B:Individual - some sub type, has custom data attached.
If a Merge is attempted between A and B CiviCRM does not display the sub-type to the user. If you say that B is the duplicate, this custom data is lost forever, without warning.

The patch attached does two things:

1. It puts the contact_sub_type after the contact's name in the merge table header – so the user can see what they are doing.
2. If contact_sub_type is set on the duplicate (the one that will be deleted), a warning is printed.

Hope this is helpful to someone else. Really glad I spotted it before my client lost data!

Rich / artfulrobot.com