[4.1] [NEW] [BUG FIX] Improved Random

I've fixed the errors introduced by @taylorotwell in laravel 4.1.28 whenever the `validMac` function was called causing: `You need to specify a file path to store the seed`.

I've improved the symfony security dependency so we only require what we actually need.

I've changed the function calls to the random method to always call the string class on suggestion by @barryvdh.

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Replaces #4175. Related to #4130. Fixes #4182 and laravel/laravel#2849.