Corrected HTTP user agent generation (branch v2)

Basically the same as #124.

> I noticed this issue when I was looking through my web server logs a few minutes ago.
>
> The product token was plain and simply poorly generated. The format ought to be \<product token\>/\<version\>, not \<product token\>-\<version\>.
>
> See [RFC 2068, section 3.8](http://tools.ietf.org/html/rfc2068#section-3.8) (HTTP 1.1) and [RFC 1945, section 3.7](http://tools.ietf.org/html/rfc1945#section-3.7) (HTTP 1.0).