Posting the unhide_users_and_fix_permissions.sh script

One side effect of the iTunes 11.2 update on Thursday, May 15th 2014
has been that some but not all Macs were seeing the /Users and
/Users/Shared folders disappear. The permissions on the /Users folder
were also changed to be world-writable, so that anyone could read and
write to the /Users folder.

After considerable investigation, it looks like the issue has been tied
to two causes:

1. iTunes 11.2 being installed
2. iCloud's Find My Mac being enabled.

The 10.9.3 update by itself does not seem to be the root cause, as the
behavior has also been reproduced on 10.9.2 with iTunes 11.2 and Find
My Mac enabled.

To fix this issue if you're seeing it:

1. Open System Preferences
2. Open the iCloud preference pane
3. Check if Find My Mac is enabled
4. If Find My Mac is enabled, uncheck it to disable it.
5. Run the unhide_users_and_fix_permissions.sh script found in this
directory.