Deliberate overriding of an existing file to tests

Deliberate overriding via `save_as` metadata should be allowed, even after the
overwrite detection feature. This commit is to add tests for deliberate
overriding. As a result, the relevant tests *should fail* after this commit.

Added a page and an article, both to override a tag, with very old dates so
it limits the amount of diff in the generated pages.

Overriding feature introduced by d0e9c52410
Overwrite detection introduced by ff7410ce2a

pelican/tests/output/basic/category/bar.html

@@ -15,6 +15,7 @@
         <header id="banner" class="body">
                 <h1><a href="/">A Pelican Blog </a></h1>
                 <nav><ul>
+                    <li><a href="/tag/oh.html">Oh Oh Oh</a></li>
                     <li><a href="/override/">Override url/save_as</a></li>
                     <li><a href="/pages/this-is-a-test-page.html">This is a test page</a></li>
                     <li class="active"><a href="/category/bar.html">bar</a></li>

pelican/tests/output/basic/category/cat1.html

@@ -15,6 +15,7 @@
         <header id="banner" class="body">
                 <h1><a href="/">A Pelican Blog </a></h1>
                 <nav><ul>
+                    <li><a href="/tag/oh.html">Oh Oh Oh</a></li>
                     <li><a href="/override/">Override url/save_as</a></li>
                     <li><a href="/pages/this-is-a-test-page.html">This is a test page</a></li>
                     <li><a href="/category/bar.html">bar</a></li>

pelican/tests/output/basic/category/misc.html

@@ -15,6 +15,7 @@
         <header id="banner" class="body">
                 <h1><a href="/">A Pelican Blog </a></h1>
                 <nav><ul>
+                    <li><a href="/tag/oh.html">Oh Oh Oh</a></li>
                     <li><a href="/override/">Override url/save_as</a></li>
                     <li><a href="/pages/this-is-a-test-page.html">This is a test page</a></li>
                     <li><a href="/category/bar.html">bar</a></li>
@@ -85,6 +86,26 @@
                 <a class="readmore" href="/unbelievable.html">read more</a>
                 </div><!-- /.entry-content -->
             </article></li>
+
+            <li><article class="hentry">
+                <header>
+                    <h1><a href="/tag/baz.html" rel="bookmark"
+                           title="Permalink to The baz tag">The baz tag</a></h1>
+                </header>
+
+                <div class="entry-content">
+<footer class="post-info">
+        <abbr class="published" title="2010-03-14T00:00:00">
+                Sun 14 March 2010
+        </abbr>
+
+<p>In <a href="/category/misc.html">misc</a>. </p>
+
+</footer><!-- /.post-info -->                <p>This article overrides the listening of the articles under the <em>baz</em> tag.</p>
+
+                <a class="readmore" href="/tag/baz.html">read more</a>
+                </div><!-- /.entry-content -->
+            </article></li>
             </ol><!-- /#posts-list -->
             </section><!-- /#content -->
         <section id="extras" class="body">

pelican/tests/output/basic/category/yeah.html

@@ -15,6 +15,7 @@
         <header id="banner" class="body">
                 <h1><a href="/">A Pelican Blog </a></h1>
                 <nav><ul>
+                    <li><a href="/tag/oh.html">Oh Oh Oh</a></li>
                     <li><a href="/override/">Override url/save_as</a></li>
                     <li><a href="/pages/this-is-a-test-page.html">This is a test page</a></li>
                     <li><a href="/category/bar.html">bar</a></li>