cache_handler does not support hyphens

[mikehedman]

In elgg.reload_all_translations, an ajax call is made to a url like:
cache/js/default/languages/en-gb.1234545.js

The problem is that when using a hyphenated language identifier (en-gb), the cache handler code rejects the request through the following filter:

only alphanumeric characters plus /, ., and _ and no '..'
$filter = array("options" => array("regexp" => "/^{(\.?[_a-zA-Z0-9\/]+)+$/"));}

Adding "\-" to the front of the filter fixes it:
$filter = array("options" => array("regexp" => "/^{(\.?[\-_a-zA-Z0-9\/]+)+$/"));}

As an aside... when this filter rejects the request, it echos back a message. But since this is being called through ajax, loading the JavaScript file fails silently...and then mysterious things start NOT working on your site.