Fix an issue where the repository symbol index would incorrectly activate inside inline comments

Summary:
See PHI185. When looking at a revision, you can Command-Click (Mac) symbols to jump to their definitions (provided the symbol index has been built).

Currently, the code works on any node inside the changeset list, so it activates when clicking links inside inline comments and opening them in a new window.

To avoid this, don't activate if we're inside an inline comment. This technically prevents you from doing a symbol lookup on a symbol inside a codeblock inside an inline, but that seems fine/reasonable.

Test Plan: Wrote Dxxx in an inline, command-clicked it. Before: got a symbol lookup. After: just a new tab with the revision.

Reviewers: amckinley

Reviewed By: amckinley

Differential Revision: https://secure.phabricator.com/D18753