Use a helper function in bakery_decrypt and bakery_encrypt

bakery_mix used to be tje unqiue function to perform crypt operations in Bakery. Recently, it has become two fucntions, bakery_decrypt and bakery_encrypt. This is good, because are easily to know how to use them than previous bakery_mix (it used a paramter to indicate which operation to perform).

But those functions have the same code except for one function call.

They should be wrappers around a helper function to makes the real work (more or less like the old bakery_mix buddy), so any changes in crypt operations is only done in one function, not in two.

Patch in progress.