[VD:LocalFileSystem] add an option statCorrector to correct stat data

Example for 32bit PHP on armv7l GNU/Linux see #2613

```php
array (
    'driver'        => 'LocalFileSystem',
    'path'          => '/path/to/files/',
    'statCorrector' => function (&$stat, $path, $statOwner,
$volumeDriveInstance) {
        if (isset($stat['size']) && $stat['mime'] !== 'directory') {
            if ($stat['size'] == '0') {
                // filesize problem for file larger than 4GB ( testing
                // in PHP Version 5.4.16)
                // https://stackoverflow.com/questions/6482211/php-filesize-over-4gb
                $stat['size'] = trim(shell_exec('stat -c %s
'.escapeshellarg($path)));
            }

            if ($stat['ts'] === false){
                // sometime filemtime will failed to return false
                $stat['ts'] = (int)trim(shell_exec('stat -c %Y
'.escapeshellarg($path)));
            }
        }
    }
)
```

php/elFinderVolumeLocalFileSystem.class.php

@@ -67,6 +67,7 @@ class elFinderVolumeLocalFileSystem extends elFinderVolumeDriver {
 		$this->options['detectDirIcon'] = '';         // file name that is detected as a folder icon e.g. '.diricon.png'
 		$this->options['keepTimestamp'] = array('copy', 'move'); // keep timestamp at inner filesystem allowed 'copy', 'move' and 'upload'
 		$this->options['substituteImg'] = true;       // support substitute image with dim command
+		$this->options['statCorrector'] = null;       // callable to correct stat data `function(&$stat, $path, $statOwner, $volumeDriveInstance){}`
 	}
 	
 	/*********************************************************************/
@@ -117,7 +118,11 @@ class elFinderVolumeLocalFileSystem extends elFinderVolumeDriver {
 		if (is_null($this->options['syncCheckFunc'])) {
 			$this->options['syncCheckFunc'] = array($this, 'localFileSystemInotify');
 		}
-		
+		// check 'statCorrector'
+		if (empty($this->options['statCorrector']) || !is_callable($this->options['statCorrector'])) {
+			$this->options['statCorrector'] = null;
+		}
+
 		return true;
 	}
 	
@@ -519,6 +524,10 @@ class elFinderVolumeLocalFileSystem extends elFinderVolumeDriver {
 			}
 		}
 		
+		if ($this->options['statCorrector']) {
+			call_user_func_array($this->options['statCorrector'], array(&$stat, $path, $this->statOwner, $this));
+		}
+
 		return $stat;
 	}
 	
@@ -738,6 +747,9 @@ class elFinderVolumeLocalFileSystem extends elFinderVolumeDriver {
 						$stat['size'] = $dir ? 0 : $size;
 					}
 					
+					if ($this->options['statCorrector']) {
+						call_user_func_array($this->options['statCorrector'], array(&$stat, $fpath, $this->statOwner, $this));
+					}
 				}
 				
 				$cache[] = array($fpath, $stat);