feature #772 Added "security.hide_user_not_found" support in SecurityServiceProvider (tomaszsobczak)

This PR was squashed before being merged into the master branch (closes #772).

Discussion
----------

Added "security.hide_user_not_found" support in SecurityServiceProvider

Added "security.hide_user_not_found" support in SecurityServiceProvider to make configuration similar with Symfony2 framework.

Commits
-------

9c614f5a Added "security.hide_user_not_found" support in SecurityServiceProvider