Fix the `pull_merge_last` and `pull_delete_last` option values that are used on merge and delete operations. This prevents a problem, that has existed since 2.1.0, with retrieving these records.

[jonathanstegall]

What does this Pull Request do?

This fixes #466. The pull_merge_last and pull_delete_last option values are supposed to be fieldmap-specific, ex object_sync_for_salesforce_pull_merge_last_Contact_2 instead of object_sync_for_salesforce_pull_merge_last_Contact. This fixes the problem with the SOQL queries that are used to detect merges and deletes.

How do I test this Pull Request?

• enable merging on a fieldmap
• merge some records that apply to that fieldmap
• see that they are merged
• do the same with deleting