Fix some small syntax errors in the Review Board docs.
Review Request #8670 — Created Jan. 26, 2017 and submitted
We had a few references and string literals that were broken, causing errors when building the Review Board documentation. This fixes those errors, and converts one set of string literal to file references.
Built the docs without errors.
Tool: Pyflakes Processed Files: reviewboard/hostingsvcs/forms.py reviewboard/diffviewer/diffutils.py Tool: PEP8 Style Checker Processed Files: reviewboard/hostingsvcs/forms.py reviewboard/diffviewer/diffutils.py