Add more files from Heimdal

Add more files from Heimdal

Add the base64 implementation from libroken, and the n-fold.c file
from libkrb5 to the list of source files that we import from Heimdal.

It also pulls in the new sha512.c and validate.c files which are now
necessary to complete a userspace hcrypto build.

This patch will fail to build until the build fixes from the subsequent
change are applied.

Change-Id: I60a691d0ccebd6d6bfb823856f79b59670eb86ec
Reviewed-on: http://gerrit.openafs.org/2897
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>