Namespace-clean some more heimdal symbols

Namespace-clean some more heimdal symbols

We get linker conflicts if we try to statically link against the
system libkrb5 when it is heimdal, from both hcrypto and rfc3961.

While here, add an include guard to hcrypto's config.h.

Change-Id: Ib5fcd9291b295415325a4ed230bd35d496961367
Reviewed-on: http://gerrit.openafs.org/11740
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>