Fix some KRB5_CALLCONV botches that were causing trouble for Windows build

Fix some KRB5_CALLCONV botches that were causing trouble for Windows build

Update send_to_kdc() to use various krb5 internals to talk to the krb4
KDC.  Add a new internal function to optionally return the local
address used to talk to the KDC.  Many changes to lib/krb5/os to
support this.  Fix bug in krb5int_sendto() that prevented correct UDP
length from being returned.  Update callers of internal locate_* and
sendto_* functions.

ticket: 1189
status: open

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@15038 dc483132-0cff-0310-8789-dd5450dbe970