heimdal 1.6rc2

Heimdal 1.5.2 and 1.5.3 fails to build on Mavericks caused by errors
with strlcpy and strlcat. Tried to patch that but new unrelated errors
occurred. Better to go forward and use the newer 1.6rc2 that builds just
fine on Mavericks.

Closes #284.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>