Urlencode the output

We must urlencode the output or the ";" in perfdata will cause errors.

see rfc1738
> Many URL schemes reserve certain characters for a special meaning: their appearance in the scheme-specific part of the URL has a designated semantics. If the character corresponding to an octet is reserved in a scheme, the octet must be encoded. The characters ";", "/", "?", ":", "@", "=" and "&" are the characters which may be reserved for special meaning within a scheme. No other characters may be reserved within a scheme.

http://www.ietf.org/rfc/rfc1738.txt

It took me a long time to realise.