krb5_kt_have_content

[Greg Hudson]

Of course, having sent that out, I just noticed another issue.  The
Heimdal API signature for krb5_kt_have_content() returns krb5_boolean,
but the actual return value is a krb5_error_code (0 or KRB5_KT_NOTFOUND).

I think the best choice here is to return krb5_error_code, which is
normally the same type (int) as krb5_boolean, and maybe suggest that
Heimdal correct its API since it should be ABI-compatible to do so.