Two small fixes in the sfPropelPlugin for newer PHP versions

I'v patched the sfPropelPlugin for newer versions of PHP that have deprecated mysql_escape_string
I've ran it with the change you have applied on php 5.5, this is the result:
```
[PHP Error] mysql_real_escape_string(): The mysql extension is deprecated and will be removed in the future: use mysqli or PDO instead [line 98 of /vendor/symfony/symfony1/lib/plugins/sfPropelPlugin/lib/vendor/propel-generator/classes/propel/engine/platform/MysqlPlatform.php]
```