Fix doctrine common dependency

[eventhorizonpl]

After release of Doctrine 2.4 the following versions was installed:
doctrine-orm: 2.3.x
doctrine-dbal: 2.3.x
doctrine-common: 2.4.x

We want the same version of doctrine components. I suggest blocking it on 2.3 for now.

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Tests pass?	yes
License	MIT

[Tobion]

1. why not allow 2.4 of orm to be installed. the changes do not seem to affect symfony. so it should be compatible
2. when 1. not desired, I don't see why we force all versions to be the same as done in this pr. if common 2.4 would not be compatible with orm 2.3, it would need to be changed in orm's composer.json, not in symfony.

[eventhorizonpl]

@Tobion

at 1) I have nothing against allowing to use doctrine 2.4. But it's up to @fabpot
at 2) official requirements for using doctrine 2.4

{
    "require": {
        "doctrine/common": "2.4.*",
        "doctrine/dbal": "2.4.*",
        "doctrine/orm": "2.4.*"
    }
}

http://www.doctrine-project.org/blog/doctrine-2-4-released.html

[Tobion]

at 2) what i mean is that this PR is bad IMO. we don't need to force doctrine-common <2.4. there is nothing wrong with installing doctrine-orm: 2.3.x and doctrine-common: 2.4.x. if it was not compatible it needs to be in the composer.json of doctrine-orm. this is what dependency and requirements resolution is about.

see https://github.com/doctrine/dbal/blob/2.3/composer.json#L16

[Tobion]

@fabpot please revert

[fabpot]

reverted