Pass the entire myuser_t* to svslogin_sts()

Some protocol modules, like nefarious, want to access other fields than
just `->name`; this avoids having to call myuser_find() just to find the
same myuser that's already known. (Ref: #248)

It does, however, change the protocol module API.
Merge pull request #249 from grawity/svslogin-myuser_t

Pass the entire myuser_t* to svslogin_sts()