use 32 bytes instead of 24 for seed material from ThreadedSeedGenerator
after seeding, pointlessly threw away the first few bytes.  Removed.
use CryptoApiRandomGenerator in addition to other entropy sources
SecureRandom ctor: given this is a sha1Generator, seed with 20 bytes instead of 8
GetInstance() returns a seeded instance. If you want an unseeded instance, you must use the unseeded ctor in which you supply your own generator
In SecureRandom, the usage of ReversedWindowGenerator only reordered the output of sha256Generator. It added computation overhead and zero cryptographic value.  Removed.