Possible OOM when accessing extension history in the admin

Something like uninstalling a XAR extension from 100 wikis in a single job (extension installed on root) generate a pretty huge history. Problem is that the history view in the admin serialize the history record directly in the HTML instead of when download is requested which generate a huge wiki content to parse. Looks like javacc go nuts and needs a lot of memory to parse this enormous html macro content (probably because of the lookhead).

It would really be better to move that serialization to the download.