Normalize frames for trace items since they can contain invalid data.

Refs https://github.com/Seldaek/monolog/pull/474/files

The fix in the previous PR did not take into account that there might be object wrapped resources that would break json_encode, so the best solution would be normalizing those frames again.

@Seldaek Sorry for the inconvenience, but our graylog is still ramming up with those json_encode error messages.

tests/Monolog/Formatter/GelfMessageFormatterTest.php

@@ -182,50 +182,6 @@ class GelfMessageFormatterTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals('pair', $message_array['_EXTkey']);
     }
 
-    /**
-     * @covers Monolog\Formatter\GelfMessageFormatter::format
-     */
-    public function testExceptionObjectWithResourceTrace()
-    {
-        if (defined('HHVM_VERSION')) {
-            $this->markTestSkipped('Not supported in HHVM since it detects errors differently');
-        }
-
-        // This happens i.e. in React promises or Guzzle streams where stream wrappers are registered
-        // and no file or line are included in the trace because it's treated as internal function
-        set_error_handler(function ($errno, $errstr, $errfile, $errline ) {
-            throw new \ErrorException($errstr, 0, $errno, $errfile, $errline);
-        });
-
-        try {
-            $resource = fopen('php://memory', '+w');
-            // Just do something stupid with a resource as argument
-            strpos($resource, 'FOO');
-        } catch (\Exception $e) {
-        }
-
-        // restore the error handler
-        restore_error_handler();
-
-        $formatter = new GelfMessageFormatter();
-        $record = array(
-            'level' => Logger::ERROR,
-            'level_name' => 'ERROR',
-            'channel' => 'meh',
-            'context' => array('from' => 'logger', 'exception' => $e),
-            'datetime' => new \DateTime("@0"),
-            'extra' => array(),
-            'message' => 'log'
-        );
-
-        $message = $formatter->format($record);
-
-        $this->assertRegExp(
-            '%\\\\"resource\\\\":\\\\"Resource id #\d+\\\\"%',
-            $message->getAdditional('ctxt_exception')
-        );
-    }
-
     private function isLegacy()
     {
         return interface_exists('\Gelf\IMessagePublisher');