System requirements

I tried using the CMF on one of our testing servers with MySQL 5.0.51 and it failed:

```
SQLSTATE[42000]: Syntax error or access violation: 1305 FUNCTION cmf-app.EXTRACTVALUE does not exist 
```

It seems the function ExtractValue() used by jackalope-doctrine-dbal was added in MySQL 5.1.5.

Reference:
- http://dev.mysql.com/doc/refman/5.1/en/xml-functions.html

@dbu already added the requirement to the jackalope-doctrine-dbal repository:
- https://github.com/jackalope/jackalope-doctrine-dbal/commit/d884ee8ac706a297aa83c9247b61ff73ed122c3d