osx: let prefpane knows where binaries can be found

osx: let prefpane knows where binaries can be found

Starting from OS X 10.11, the OpenAFS binaries were moved to the
following directories: /opt/openafs/bin and /opt/openafs/sbin. However,
the OpenAFS prefpane is not aware of the change mentioned above. As a
result, some functionalities provided by the OpenAFS prefpane are not
working properly.

To fix this problem, add the new paths to the proper environment
variable.

Change-Id: Idaa2f0329af2092cf9ad1d63f1a01300b150227a
Reviewed-on: https://gerrit.openafs.org/12507
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>