Merge sphinx-contrib#50: Sphinx 1.6 compat

StandaloneHTMLBuilder.default_sidebars was removed in sphinx ~1.6.

sphinx-doc/sphinx@e8e63b1

Get the side bar from the theme instead when possible.

Fixes sphinx-contrib#42

sphinxcontrib/versioning/sphinx_.py

@@ -62,7 +62,7 @@ def builder_inited(app):
             try:
                 app.config.html_sidebars['**'] = StandaloneHTMLBuilder.default_sidebars + ['versions.html']
             except AttributeError:
-                app.config.html_sidebars['**'] = ['versions.html']
+                app.config.html_sidebars['**'] = StandaloneHTMLBuilder(app).get_theme_config()[1].get('html_sidebars', []) + ['versions.html']
         elif 'versions.html' not in app.config.html_sidebars['**']:
             app.config.html_sidebars['**'].append('versions.html')