js_user.c

Much easier and more accurate way to determine (via JS) if a specific user
has a particular kind of access to a message sub-board or a file directory.
This is accurate because it uses the 'userdat' functions under the hood, which
check much more than just a single access requirement string against the user.

Usage:
bool can_access_sub(string sub_code or number sub_num
 [,'read', 'post', or 'operator'])
bool can_access_dir(string dir_code or number dir_num
 [,'download', 'upload', or 'operator'])

If no access string (second argument) is specified, then just generic "access"
(e.g. for listing areas) is checked.

The existing msg_area.sub[].can_access, can_read, can_post (and similar for
file_area.dir[]) are still useful, but only for the current 'user'. If you
want to check a different user's access to a sub-board or file directory, you
really need to use these new User class methods.