Fix history link in Diffusion non-root browse views

Summary:
Fixes T9798. That task has good repro instructions.

In sub-views, we don't link the "History" icon correctly -- we only link it to history/README instead of history/path/to/README. Add the full path.

Also canonicalize the paths in a slightly prettier and more consistenty way.

Test Plan: Viewed root and non-root browse tables, saw links show up properly.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9798

Differential Revision: https://secure.phabricator.com/D14491