`krb5_principal_get_comp_string' that returns parts of a principal;
this is a replacement for the internal `krb5_princ_realm' and
`krb5_princ_component' macros that everyone seem to use
git-svn-id: svn://svn.h5l.se/heimdal/trunk/heimdal@10136 ec53bebd-3082-4978-b11e-865c3cabbd6b