Make lockIDSet readable by mortals

Make lockIDSet readable by mortals

The lockIDSet function was a sprawling mess of #ifdefs. This change
consolidates it so there is completely different function for each
platform, with some internal #ifdefs remaining for platform-specific
variations. The side effect of this is that the function is now readable.

Reviewed-on: http://gerrit.openafs.org/164
Reviewed-by: Russ Allbery <rra@stanford.edu>
Tested-by: Russ Allbery <rra@stanford.edu>