clean up axscache at shutdown

clean up axscache at shutdown

modify allocations in axscache code to be able to be tracked. at shutdown,
clean up allocations.

Change-Id: I1fbde0fe49cf0cdeea451dac58718a90f1c87e66
Reviewed-on: http://gerrit.openafs.org/1037
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>