Fix a segfault with StripDown and the :quote option

Since the `StripDown` render extends from `Base`, every available
callback should be defined to avoid segmentation faults since the
C code assumes that it **doesn't** deal with a `Base` object.

Fixes #639.

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+* Fix a segfault rendering quotes using `StripDown` and the `:quote`
+  option.
+
+  Fixes #639.
+
 * Fix `warning: instance variable @options not initialized` when
   running under verbose mode (`-w`, `$VERBOSE = true`).
 

lib/redcarpet/render_strip.rb

@@ -13,7 +13,7 @@ class StripDown < Base
         :autolink, :codespan, :double_emphasis,
         :emphasis, :underline, :raw_html,
         :triple_emphasis, :strikethrough,
-        :superscript, :highlight,
+        :superscript, :highlight, :quote,
 
         # footnotes
         :footnotes, :footnote_def, :footnote_ref,

test/stripdown_render_test.rb

@@ -58,4 +58,12 @@ def test_highlight
 
     assert_equal expected, output
   end
+
+  def test_with_quote_option_enabled
+    markdown = %(A common idiom is "Hello world")
+    expected = %(A common idiom is Hello world)
+    output   = render(markdown, with: [:quote])
+
+    assert_equal expected, output
+  end
 end