mgI18nPlugin pdo support

some upgrade on the plugin.

A new version of the mgI18nPlugin is now available, this version comes with many bugs fixes and improvements:

• remove Doctrine dependency : PDO is used for fast translation retrieving and ORM compatibilities
• add a new database tab, the user can now lookup the database for messages
• learning mode option : when this settings is set to true all messages are saved into the database
• the xliff import task now update target if the target is already in the database

Versions:

• symfony 1.2 : UPGRADE , README
• symfony 1.3/1.4 : UPGRADE , README

This version will be the last one available for symfony 1.2.