From: Kevin Coffman <kwc@citi.umich.edu>

Consolidate some of the Kerberos checking instead of repeating
the same things for MIT and Heimdal.
Also adds more checks to distinguish 32-bit from 64-bit
(mainly for gssapi.h)
Fix svcgssd Makefile so make TOP=../../ works correctly there.
Enable running a modern autoheader.

(Requires that autoconf be run to regenerate configure script.)