Alter responder function signature for consistency

For the responder callback signature, put the closure argument just
after the context, and use KRB5_CALLCONV.  These changes make the
signature consistent with most other libkrb5 callbacks.

https://github.com/krb5/krb5/commit/8450ead695639f09862fdcecd46530b1d1b59bfe
Author: Greg Hudson <ghudson@mit.edu>
Commit: 8450ead695639f09862fdcecd46530b1d1b59bfe
Branch: master
 src/include/krb5/krb5.hin   |    6 +++---
 src/lib/krb5/krb/preauth2.c |    4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)