Allow backtick-quoting of <pre> tags.

The backwards-compatibility fix for code like:

    Here's the code example:<pre><code>
    alert("Blah");
    </code></pre>

was a bit too lose.  So tightened it up to only apply in case
where the <pre> or <pre><code> is at the end of line.

Fixes: #380

lib/jsduck/doc_formatter.rb

@@ -67,7 +67,7 @@ def format(input)
       # normal Markdown, which often causes nested <pre>-blocks.
       #
       # To prevent this, we always add extra newline before <pre>.
-      input.gsub!(/([^\n])<pre>/, "\\1\n<pre>")
+      input.gsub!(/([^\n])<pre>((<code>)?$)/, "\\1\n<pre>\\2")
 
       # But we remove trailing newline after <pre> to prevent
       # code-blocks beginning with empty line.

spec/doc_formatter_spec.rb

@@ -494,6 +494,26 @@ def get(filename)
       end
     end
 
+    describe "quoted `<pre>`" do
+      before do
+        @html = @formatter.format("Some `<pre>` in here.")
+      end
+
+      it "is correctly escaped" do
+        @html.should == "<p>Some <code>&lt;pre&gt;</code> in here.</p>\n"
+      end
+    end
+
+    describe "quoted `<pre><code>`" do
+      before do
+        @html = @formatter.format("Some `<pre><code>` in here.")
+      end
+
+      it "is correctly escaped" do
+        @html.should == "<p>Some <code>&lt;pre&gt;&lt;code&gt;</code> in here.</p>\n"
+      end
+    end
+
     shared_examples_for "example" do
       it "creates <pre> with inline-example class" do
         @html.should =~ /<pre class='inline-example *'>/m