conv_princ.c (krb5_425_conv_principal): Use new calling

conv_princ.c (krb5_425_conv_principal): Use new calling
	convention of krb5_get_realm_domain, which is that it
	returns the realm *without* the leading dot.

	Also use the profile code to look up individual instance
	conversions using [realms]/<realm>/v4_instance_convert/<inst>
	This allows special case handling of mit.edu and
	lithium.lcs.mit.edu.

t_kerb.c: New file for testing krb library functions.  Currently
	only tests krb5_425_conv_principal.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@5726 dc483132-0cff-0310-8789-dd5450dbe970