debian zoneinfo link fix

[Jakob Østergaard]

Dear list,

I need to specify the path explicitly for reread-timezone-repository, since the default doesn’t work the way I deploy my system.

So I have a line like:
 (local-time:reread-timezone-repository :timezone-repository "/usr/share/zoneinfo/“)

Unfortunately, on Debian 7 at least, /usr/share/zoneinfo/ contains a symlink “localtime” which points back to /etc/localtime.

This causes reread-timezone-repository to fail (it calls subseq with an invalid index).

The following patch is a simple fix; it simply ignores files outside of the root.

Patch attached.