Add repository browser for Kiln Harmony

Fog Creek's Kiln now supports Git.  This repository browser
implementation borrows heavily from the GithubWeb and CGit browsers.
[SECURITY] Use ACL.impersonate to avoid a race condition giving elevated privileges.
Merge pull request #150 from chrisklaiber/kiln-repo-viewer

Add repository browser for Kiln Harmony
Merge branch 'master' into master_ialbors