Returns a vector describing the passwd entry for the given user. who may be either a string, in which case it is interpreted as a login name, or an integer, in which case it is interpreted as a user id.
Returns #f if the lookup fails.
The returned vector has 7 elements: The user login name, the user id, the user's primary group id, their home directory, their shell, their encrypted passwd, and their GECOS data. Some data may not be available, in which case #f is present in that slot.