#61: Address a regression in the original fix

[jeremystretch]

Fixes: #61

• Revert the change in Fixes #61: Fix transaction rollback when performing a dry run sync #65
• Pass the branch's connection to transaction.atomic() to ensure transaction support

[arthanson]

It works in the original repro scenario, but it also works in the original code as it has the fix for 61 in it. So it seems to work, just not sure the fail scenario.