Split crypto_global_init() into pre/post config

Split crypto_global_init() into pre/post config

It's increasingly apparent that we want to make sure we initialize our
PRNG nice and early, or else OpenSSL will do it for us.  (OpenSSL
doesn't do _too_ bad a job, but it's nice to do it ourselves.)

We'll also need this for making sure we initialize the siphash key
before we do any hashes.