added Form::open_multipart and tweaked Upload_of rule.

system/form.php

@@ -50,6 +50,20 @@ class Form {
 		return $html.PHP_EOL;
 	}
 
+	/**
+	 * Open a HTML form that accepts file uploads.
+	 *
+	 * @param  string  $action
+	 * @param  string  $method
+	 * @param  array   $attributes
+	 * @return string
+	 */	
+	public static function open_multipart($action = null, $method = 'POST', $attributes = array())
+	{
+		$attributes['enctype'] = 'multipart/form-data';
+		return static::open($action, $method, $attributes);
+	}
+
 	/**
 	 * Close a HTML form.
 	 *
@@ -100,7 +114,6 @@ class Form {
 	public static function label($name, $value, $attributes = array())
 	{
 		static::$labels[] = $name;
-		
 		return '<label for="'.$name.'"'.HTML::attributes($attributes).'>'.HTML::entities($value).'</label>'.PHP_EOL;
 	}
 

system/validation/rules/upload_of.php

@@ -1,5 +1,6 @@
 <?php namespace System\Validation\Rules;
 
+use System\File;
 use System\Input;
 use System\Validation\Rule;