cleanup errors on kadmin object

new error model for principal objects

remove remaining instances of old error handling.

restore direct error numbers (lower errno values are possible); cleanup memory leaks

track internal lock state; only unlock on dealloc if lock is held.

krb5_init leaks memory - same result running kadmin.local: unsupported command

when resolving the client_name from a credential cache we are responsible for freeing allocated memory

valgrind supp file for python leaks.

restructure assignment so no memory is allocated until argumets are parsed.