Import of code from heimdal

Import of code from heimdal

This commit updates the code imported from heimdal to
987658325eb7bd6b10882cc4cdd224499e7f7a03 (switch-from-svn-to-git-2052-g9876583)

New files are:
	roken/getdtablesize.c

Upstream changes are:

Love Hornquist Astrand (2):
      prefix symbols that are _krb5_ structures
      prefix internal structures with _krb5_

Change-Id: I36aae13d877b6b40b8d2db47217884dc24f3f9c8
Reviewed-on: http://gerrit.openafs.org/4339
Tested-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Derrick Brashear <shadow@dementia.org>