Report verbose error messages from KDC

Report verbose error messages from KDC

We were losing verbose error messages when logging from the KDC because
the context passed to krb5_klog_init did not match the realm-specific
context used for most library function calls.  Introduce a wrapper
function kdc_err which copies the error state from the call context
to the log context.  The wrapper function also knows the program name,
which removes the need to pass argv[0] around everywhere or make up
program names.

ticket: 6408
target_version: 1.7
tags: pullup

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@22079 dc483132-0cff-0310-8789-dd5450dbe970