R1:9d84eb4c747d

Allow Conduit API methods in Diffusion to accept any repository identifier

Summary:
Ref T4245. Broaden support to include "ABCD", "rABCD", "1234", "R1234", etc.

This doesn't change the old behavior, just accepts more stuff.

Test Plan:
- Browsed Diffusion.
- Made various calls via API console.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4245

Differential Revision: https://secure.phabricator.com/D14928