Merge duplicate contacts gives no control over merging of Grants

The user cannot control if Grants are preserved when merging contacts

Reproducible on Drupal demo r23950

Steps to reproduce.
1. Create a contact
2. Add a grant
3. Create a second contact that will match the first on a dedupe rule (eg, same first name and last name)
4. Find duplicates using that rule
5. Select the pair for merging
6. Make the contact with the grant the duplicate
7. Note that grants are not listed as data to be preserved, so the user has no control over whether they are merged or not
8. Merge the contacts
9. Note that the merged contact has the grant from the duplicate

PS: This affects 3.0.2, but that option wasn't supplied in the dropdown list