generator/html: fix ocaml code example syntax highlight
generator/html: fix ocaml code example syntax highlight

Caml2html outputs a string containing html tags, which were escaped by
Cow, and therefore the HTML source of the syntax-highlighted OCaml code
was displayed as plain text.

Signed-off-by: Gabor Igloi <7535f5501fd71876c93d896691e178fd3a11cfbb@citrix.com>

xapi-project/message-switch,xapi-project/message-switch,xapi-project/message-switch