krb4 library major version bump

[Tom Yu]

>>>>> "lxs" == Alexandra Ellwood <lxs at MIT.EDU> writes:

lxs> The KfM 4.5.x and 4.0.x ABI defines and exports krb_err_txt as:

lxs> extern const char * const * krb_err_txt;

lxs> This includes the unchangeable CFM ABI.  So to preserve ABIs on KfM,
lxs> we will need to usea different mechanism on the Mac.  Sigh.

We could also make a platform-specific ABI for the Mac... we certainly
already have platform-specific ABI differences for struct credentials.

---Tom