Unfortunately, pre-1.7 krshd fails to support keyed checksums because

Unfortunately, pre-1.7 krshd fails to support keyed checksums because
it uses the wrong API and wrong key usage.  So, if the auth_context
has an explicit checksum type set, then respect that.  kcmd sets such
a checksum type.  Also, because other applications may have the same
problem, allow the config file variable if set to override the default
checksum.

* kcmd.c: Force use of rsa_md5
* init_ctx.c: do not default  to md5
* mk_req_ext.c: allow auth_context to override

ticket: 1624

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@22160 dc483132-0cff-0310-8789-dd5450dbe970