DSR computation: Handle <ref> tags nested in <references>

* The current fix is a hack to fix dsr issues right away.
  Meanwhile, will invesitigate a fix that will involve processing
  <references> in its own subpipeline and persisting state into
  the top-level page.

* Fixes a known selser failure from bug 62025.

Change-Id: I0f80d68e927f500939a44af401cc73c07e24721f