2842. [func] Prevent dnssec-keygen and dnssec-keyfromlabel from

2842.	[func]		Prevent dnssec-keygen and dnssec-keyfromlabel from
			creating key files if there is a chance that the new
			key ID will collide with an existing one after
			either of the keys has been revoked.  (To override
			this in the case of dnssec-keyfromlabel, use the -y
			option.  dnssec-keygen will simply create a
			different, noncolliding key, so an override is
			not necessary.) [RT #20838]