Make file handles have "/Fxxx" as the URI

Summary:
Primarily, this fixes searching for `F123` in global search.

The info URI is now a better URI than the "best" URI for files, and doesn't have redirect issues.

Test Plan: Searched for `F123` in global search.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D10330