[krbdev.mit.edu #1288] v4 ticket file format incompatibilities

[Ken Raeburn via RT]

See attached message.  The issue_date value is stored as a "long" in
the current krb5 tree.  This also causes problems when mixing apps
compiled for sparcv7 and sparcv9, or (presumably, but unconfirmed)
ia32 and ia64.  jhawk suggests investigating whether the library can
be made to support both formats, and I agree.

Looking for the four zero-valued bytes (before or after the issue
date, depending on host byte order) is probably all it would take
(until 2038, and then we get other problems), though we should still
think about what format should be used for writing on various
platforms to ease the transition.

Ken