Fix two issues with Differential updates and Owners

Summary:
Ref T13114.

• Followup fix for D19267, which didn't work correctly with new revision creation.
• Followup fix for changes in T11015. Some of the querying logic was still handling "/x.y" and "/x.y/" differently. Instead, normalize consistently to "/x.y/"

Test Plan:

• Created a new revision cleanly.
• Created a package owning only a example.txt file and saw Differential find it as an owning package in the table of contents.

Maniphest Tasks: T13114

Differential Revision: https://secure.phabricator.com/D19268