[krbdev.mit.edu #2755] push yarrow locking down into the yarrow code to reduce contention

[Ken Raeburn via RT]

> The alpha-netbsd build is failing nightly tests with:
> assertion "(&(&_m->os)->n)->initialized == K5_MUTEX_DEBUG_INITIALIZED"
> failed: file "yarrow.c", line 174, function "krb5int_yarrow_init"

Oops again.  This checkin should fix that:

2004-11-17  Ken Raeburn  <raeburn at mit.edu>

	* prng.c (do_yarrow_init): Move mutex initialization here.
	(krb5int_prng_init): Don't do it here.

lib/crypto/prng.c 5.22
lib/crypto/ChangeLog 5.171