Fixes #497: ignore case difference between tags

While retrieving all tags, case differences will be ignored.
This affects:

  * tag cloud
  * tag autocompletion

tests/FeedBuilderTest.php

@@ -93,7 +93,7 @@ class FeedBuilderTest extends PHPUnit_Framework_TestCase
         $this->assertContains('Permalink', $link['description']);
         $this->assertContains('http://host.tld/?WDWyig', $link['description']);
         $this->assertEquals(1, count($link['taglist']));
-        $this->assertEquals('stuff', $link['taglist'][0]);
+        $this->assertEquals('sTuff', $link['taglist'][0]);
 
         // Test URL with external link.
         $this->assertEquals('https://static.fsf.org/nosvn/faif-2.0.pdf', $data['links']['20150310_114633']['url']);

tests/LinkDBTest.php

@@ -290,7 +290,9 @@ class LinkDBTest extends PHPUnit_Framework_TestCase
                 'stallman' => 1,
                 'free' => 1,
                 '-exclude' => 1,
-                'stuff' => 2,
+                // The DB contains a link with `sTuff` and another one with `stuff` tag.
+                // They need to be grouped with the first case found (`sTuff`).
+                'sTuff' => 2,
             ),
             self::$publicLinkDB->allTags()
         );
@@ -310,7 +312,7 @@ class LinkDBTest extends PHPUnit_Framework_TestCase
                 'w3c' => 1,
                 'css' => 1,
                 'Mercurial' => 1,
-                'stuff' => 2,
+                'sTuff' => 2,
                 '-exclude' => 1,
                 '.hidden' => 1,
             ),

tests/utils/ReferenceLinkDB.php

@@ -21,7 +21,7 @@ class ReferenceLinkDB
             'Stallman has a beard and is part of the Free Software Foundation (or not). Seriously, read this.',
             0,
             '20150310_114651',
-            'stuff'
+            'sTuff'
         );
 
         $this->addLink(