Improve kdb5 error when default realm is unset

When the default realm name is unspecified, and none was set in the
krb5_context object, return KRB5_CONFIG_NODEFREALM from libkdb5
instead of the confusing KRB5_KDB_DBTYPE_NOTFOUND.  To accomplish
this, make kdb_get_library_name() return a krb5_error_code.

https://github.com/krb5/krb5/commit/4131988dec0199287765e1875fe0bbd375656a62
Author: Greg Hudson <ghudson@mit.edu>
Commit: 4131988dec0199287765e1875fe0bbd375656a62
Branch: master
 src/lib/kdb/kdb5.c |   20 +++++++++++++-------
 1 files changed, 13 insertions(+), 7 deletions(-)