Fix $configuration->setAutoGenerateProxyClasses() when option is boolean TRUE

I've just switched to using Yaml for configuration files (using symfony/yaml 2.3):

In `startORMConfiguration()` (and `startODMConfiguration`) the value of `$config['proxy']['autoGenerateClasses']` will be an actual boolean. When that boolean is TRUE, this check:

    in_array($config['proxy']['autoGenerateClasses'], array("0", "false", false))

Will return TRUE (because of type-casting inside `in_array()`).
Therefor the call to `$configuration->setAutoGenerateProxyClasses()` will actually disable autogeneration when `$config['proxy']['autoGenerateClasses']` is TRUE.

This PR fixes that :)