Cookies: avoid timezone confusion

Cookies date are always in GMT time. Using mktime wrongly converts them
as local time instead. This would lead to cookies expiring too early or
too late.
FileRequest: set the mime type early.

WebKit may use the MIME type during incremental loading, so we better
set it before we start feeding the data.
Remove display_mode_hook hack.

We'd better find a cleaner way to implement this, if actually needed.
LocaleRoster: race condition on catalog loading.

Using a vint32 isn't enough to safely decide if the catalog is
initialized or not. Use init_once features instead.