Having the value stored here is somewhat pointless, so this is one step
in fixing the locale handling.  Locale should be handled by the modules
themselves with their own loaded locale lookup information.

This doesn't add FLV file output to the user interface yet, but we'll
get around to that eventually.  This just adds an FLV output type.

Also, removed ftello/fseeko because off_t is a really annoying data
type, and I'd rather have a firm int64_t for large sizes, so I named it
to os_fseeki64 and os_ftelli64 instead, and changed the file size
function to return an int64_t.