windows: afsauthent.dll export afsconf_ functions

Export additional afsconf_ functions required for asetkey

Change-Id: Id8d63f7d18563bd8963750aed6b7baaf873716a8
Reviewed-on: http://gerrit.openafs.org/10069
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Windows: define HAVE_KRB5_CREDS_SESSION

Windows builds against the Kerberos Compatibility SDK which uses
the Heimdal API.  Define HAVE_KRB5_CREDS_SESSION.

Change-Id: I389cb3e8d79846c94884ea9a786e2ae0f52fa293
Reviewed-on: http://gerrit.openafs.org/10071
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>