Import of code from heimdal

Import of code from heimdal

This commit updates the code imported from heimdal to
ee7340860a22f81fb869cc431efc1fd4e5c77d34 (switch-from-svn-to-git-2542-gee73408)

Upstream changes are:

Jeffrey Altman (2):
      Windows: fallback to PROV_RNG if no PROV_RSA_FULL
      roken: posix errnos for windows

Love Hornquist Astrand (3):
      drop __restrict to please old compilers
      add krb5_is_enctype_weak
      Don't export tests from library, reported in bug from Tom Payeire

New files are:
	roken/setenv.c
	roken/unsetenv.c

Change-Id: I7e3b3db2a58eaaae9de91431565176921d79af3b
Reviewed-on: http://gerrit.openafs.org/5798
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>