weblib.php breaks upper-case hex Numeric Character References

Function format_string in lib/weblib.php has a regexp for converting lone ampersands to & It is designed to ignore HTML entities and NCR's, if these are used to represent foreign characters, but it does not ignore hex NCR's where the hex alpha characters are upper case. However, it appears that hex NCR's are allowed to be case-insensitive (http://www.w3.org/International/questions/qa-escapes).

I attach a patch to allow the regexp to ignore hex NCR's with upper case alpha characters, and hope that this is of use.