Adds support for the Doctrine ArrayCache provider.

When Doctrine is initialized via the Setup class in non-development mode, use of the NullProvider included with this package will typically force Doctrine to use the ArrayCache provider by default.  However, if at least one of the APC, XCache, Memcache, or Redis modules have been loaded, the Doctrine setup routine assumes it should be used and attempts to connect.

In cases where you actually want to use the ArrayCache provider in non-development environments, you are subsequently unable to.  This set of changes includes a doctrine-laravel ArrayProvider that allows use of the Doctrine ArrayCache provider in non-development modes, regardless of whether conflicting cache modules have been loaded.