Import of code from heimdal

Import of code from heimdal

This commit updates the code imported from the external
heimdal git repository to their revision
48ad3e1e6597f03cce5439831ef94b5ec11894e9
which is described as switch-from-svn-to-git-1593-g48ad3e1

This import was manually modified to preserve our current local
fix for sha512.c

Change-Id: Ie020beb7324469d33b85ac4c559cc473f2728d19
Reviewed-on: http://gerrit.openafs.org/2903
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>