Don't hide equations, except in MarkdownMML and MarkdownPNG

In other engines, e.g. textile, the equation delimiters have no
special meaning. So they should not be used to hide content from
wiki processing.

lib/wiki_content.rb

@@ -120,6 +120,7 @@ class WikiContent < String
 
   DEFAULT_OPTS = {
     :active_chunks       => ACTIVE_CHUNKS,
+    :hide_chunks         => HIDE_CHUNKS,
     :engine              => Engines::MarkdownMML,
     :engine_opts         => [],
     :mode                => :show
@@ -138,6 +139,8 @@ class WikiContent < String
     @options[:engine] = Engines::MAP[@web.markup]
     @options[:engine_opts] = [:filter_html, :filter_styles] if @web.safe_mode?
     @options[:active_chunks] = (ACTIVE_CHUNKS - [WikiChunk::Word] ) if @web.brackets_only?
+    @options[:hide_chunks] = (HIDE_CHUNKS - [Literal::Math] ) unless
+                  [Engines::MarkdownMML, Engines::MarkdownPNG].include?(@options[:engine])
 
     @not_rendered = @pre_rendered = nil
 
@@ -169,7 +172,7 @@ class WikiContent < String
     copy = WikiContentStub.new(self, @web, @options)
     @options[:engine].apply_to(copy)
 
-    copy.inside_chunks(HIDE_CHUNKS) do |id|
+    copy.inside_chunks(@options[:hide_chunks]) do |id|
       @chunks_by_id[id.to_i].revert
     end
   end

test/unit/page_renderer_test.rb

@@ -330,6 +330,15 @@ END_THM
         "should we go ThatWay or $ThisWay$.")
   end
   
+  def test_content_with_wikiword_in_equations_textile
+    set_web_property :markup, :textile
+    assert_markup_parsed_as(
+      "<p>$$<span class='newWikiWord'>foo<a href='../show/foo'>?" +
+      "</a></span>$$<br/>$<span class='newWikiWord'>foo<a " +
+      "href='../show/foo'>?</a></span>$</p>",
+      "$$[[foo]]$$\n$[[foo]]$")
+  end
+  
   # wikiwords are invalid as styles, must be in "name: value" form
   def test_content_with_wikiword_in_style_tag
     assert_markup_parsed_as(