fix tile update not working due to locale issues.
On systems with a locale set to something different to C or POSIX it might happen that sort fails on LC_NUMERIC interpreting comma as a thousand-separator. For example en_US.UTF-8 is such a locale where sort will fail. Result is that script no longer updated oldest tiles. This patch sets locale for the script to C in a portable way.


git-svn-id: http://svn.openstreetmap.org/applications/utils/tirex@30540 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4