redo internationalization to avoid unnecessary network lookups, and to deal with timeouts

i18n code currently checks to see whether internationalized html page is present by opening a URL. There are several problems:

• in load balancer situations, the server itself may not be able to open a URL that the user can open
• if the URL doesn't work, the system freezes

Solutions:

• do a context lookup to find the file, rather than going through a URL, unless the user explicitly supplies a URL to replace the built-in documents
• use a timeout, and log failure with an explanation