R1:7c4c76d32a3f

Fix a Quicksand/Lightbox contention issue

Summary:
Fixes T11785. Lightbox calls `JX.Stratcom.pass()` to let other handlers react, but should not. At least today, we never put, e.g., links inside a lightbox.

This code appears in the original commit so it was probably just copy/pasted from somewhere and I missed it in review.

(Or there's some edge case I'm not thinking of and we'll figure it out soon enough.)

Additionally, blacklist `/file/data/` from Quicksand naviagtion: Quicksand should never fetch…