R1:1844a6f72862

Get the correct uri_path for a diffusion request.

Summary: there is a bug in getting the uri path. When the user clicks
a line number twice, the new rev number and the line number is attached
to the end of the original uri instead of substituting it.

Test Plan: clicking line number multiple times, for both git and svn.

Reviewers: epriestley

CC:

Differential Revision: 84