add `iam' as a target.

Notes:
Sat Feb 18 09:27:17 EST 2006 rsc
    I'm more inclined just to remove iam.
    It was only used on the bitsy, and I think
    factotum supercedes it.
    


Reference: /n/sources/patch/sorry/auth-mkfile-for-iam
Date: Sat Feb 18 05:50:24 CET 2006
Reviewed-by: rsc

--- /sys/src/cmd/auth/mkfile	Sat Feb 18 05:50:14 2006
+++ /sys/src/cmd/auth/mkfile	Sat Feb 18 05:50:12 2006
@@ -11,6 +11,7 @@
 	cron\
 	debug\
 	guard.srv\
+	iam\
 	keyfs\
 	login\
 	netkey\