Update docs for the escape option in CakeNumber::currency()

Unfortunately, using actual bytes creates a host of problems for sites
not using UTF-8. Update the documentation to reflect reality, as
changing reality could cause more problems than it solves.

Closes #3351

lib/Cake/Utility/CakeNumber.php

@@ -211,7 +211,10 @@ protected static function _numberFormat($number, $places = 0, $decimals = '.', $
  * - `decimals` - Decimal separator symbol ie. '.'
  * - `negative` - Symbol for negative numbers. If equal to '()',
  *   the number will be wrapped with ( and )
- * - `escape` - Should the output be htmlentity escaped? Defaults to true
+ * - `escape` - Should the output be escaped for html special characters.
+ *   The default value for this option is controlled by the currency settings.
+ *   By default the EUR, and GBP contain HTML encoded symbols. If you require non HTML
+ *   encoded symbols you will need to update the settings with the correct bytes.
  *
  * @param float $number
  * @param string $currency Shortcut to default options. Valid values are