title: json_decode() returns null issues
body: <p>I've an issue with my JSON. It works returns correctly in PHP 5.3 (so I can't use json_last_error()), and it returns successfully when I copy string explicitly into json_decode (json_decode('{...}'). It only returns null in when I pass the result as a variable and I'm using php 5.2, which is what I need it for.</p>
  
  <p>The output comes from JSON logging in PHPUnit:</p>
  
  <pre><code>[
      {
          "event": "suiteStart",
          "suite": "",
          "tests": 2
      },
      {
          "event": "suiteStart",
          "suite": "TagTestCase",
          "tests": 2
      },
      {
          "event": "test",
          "suite": "TagTestCase",
          "test": "TagTestCase::test_it",
          "status": "fail",
          "time": 0.00248718261719,
          "trace": [
              {
                  "file": "\/UnitTest\/PHPUnit.php",
                  "line": 98,
                  "function": "run",
                  "class": "PHPUnit_Framework_TestSuite",
                  "type": "-&gt;",
                  "args": [
                      {
  
                      }
                  ]
              },
              {
                  "file": "\/UnitTest\/PHPUnit.php",
                  "line": 116,
                  "function": "run",
                  "class": "PHPUnit",
                  "type": "-&gt;",
                  "args": [
  
                  ]
              },
              {
                  "file": "\/UnitTest\/PHPUnit.php",
                  "line": 212,
                  "function": "__tostring",
                  "class": "PHPUnit",
                  "type": "-&gt;",
                  "args": [
  
                  ]
              }
          ],
          "message": "false assertionzzzzz.\nFailed asserting that &lt;boolean:false&gt; is true."
      },
      {
          "event": "test",
          "suite": "TagTestCase",
          "test": "TagTestCase::test_two",
          "status": "pass",
          "time": 0.00182914733887,
          "trace": [
  
          ],
          "message": ""
      }
  ]
  </code></pre>
  
  <p>EDIT: These are the paths, I've been exploring - maybe you are a better explorer..
  Three possible paths that could help:</p>
  
  <ul>
  <li>What is different about json_decode() in php 5.2 then 5.3? what did they change?</li>
  <li>Someone else using JSON from PHPUnit, and how they parse it.</li>
  <li>What changes when you have it in a variable vs. printing it to screen and copying it into json_decode()</li>
  </ul>
  
  <p>Any help would be greatly(!) appreciated.</p>
  
  <p>Thanks!
  Matt</p>