r23390: First part of the patch to make Apple's life easier.

r23390: First part of the patch to make Apple's life easier.
Doing this in two stages to make it very easy to
review. Context switching must look like :

gain_root();
sys_setgroups(ngroups, groups);
become_id(uid, gid);

Re-arrange order so these three calls are always
seen together.

Next will be to turn these into a function.

Jeremy.
(This used to be commit eb537185ee4a3f460709267c843c9303a9bb61b5)