macos 10.6 64 bit support

macos 10.6 64 bit support

support 64 bit userland with 32 bit kernel, and
32 and 64 bit userland with 64 kit kernel

Reviewed-on: http://gerrit.openafs.org/343
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 81099c479e148a103dcf9f4def125b28e989107c)
Reviewed-on: http://gerrit.openafs.org/362