[krbdev.mit.edu #2941] krb5-1.4 is unbuildable on HPUX 10.20

[Tom Yu via RT]

It may be worth noting that the recommended invocation of the HP-UX
C compiler, 'cc -Ae', defines '-D_HPUX_SOURCE', which turns on most of
the extended namespace.  By default the headers on HP-UX provide a
very restricted namespace.

---Tom