restructure kadmin.c to correctly handle errors and avoid memory leaks

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.