Make travis pass on Symfony 2.2

Make travis actually update the lock file and install the 2.2 components.
Document deprecation of getClassMetadata in validator docs.
Add symfony/property-access require for 2.2

This gives an actual good version of symfony/form instead of some old beta.
merged branch igorw/2.2-tests (PR #639)

This PR was merged into the master branch.

Commits
-------

6e8d404 Add symfony/property-access require for 2.2
337a92c Make travis pass on Symfony 2.2

Discussion
----------

Make travis pass on Symfony 2.2

Make travis actually update the lock file and install the 2.2 components.
Document deprecation of getClassMetadata in validator docs.