Solve issue #114.
Add Basque language also to list of known language names.

Fixes a notice on page load.
Make sure no empty name ends up in remote metadata for IdPs or SPs.
Avoid calling SimpleSAML_Utilities::normalizeURL() twice when we are redirecting and need to check if the URL is trusted.
Remove extra URL validation as normalizeURL() will have done that already. Return an empty string if the input URL is empty (disregarding its type). This should make the checkURLAllowed() function transparent and avoid it returning the current URL (normalized) when input is empty. Fixes #99.
Fix client-certificate match if-check

`preg_match` returns `0` if no matches are found, `FALSE` only on error. This means that with the previous check unmatching certificates would not be identified, only when the preg_match itself would error.