Fixed three problems in the database rename function:

Fixed three problems in the database rename function:
1. Added a missing call to krb5_dbm_db_end_update to ensure the lock file
	timestamp is updated.
2. Corrected the test for a valid lock file handle to be >=0 not non-zero.
3. Use the lock file of the target name, since the source will shortly
	disappear and another process may already be checking for the lock
	file of the target.  (For example, a kdb5_edit db load will use
	a temporary name and rename the db to the proper name when it is
	done, and krb5kdc will be testing for the target lock file.)

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@7351 dc483132-0cff-0310-8789-dd5450dbe970