Fix bug in shadowing of default sort key

* Bug introduced by 7da439e6 -- looks like I didn't test the
  examples in the commit summary after later amends of the patch.

  {{DEFAULTSORT:foo}} shadowed the 'foo' key with 'foo}}' because
  of a bad regexp that extracted the key from the source.

Change-Id: Ife44147de2a1f2ab32904b46c377b77ec600ed14
Merge "Fix bug in shadowing of default sort key"