Add libuserdefs and use in cmd/{oamuser,passwd}

*** 93,104 ****
  extern int putusrdef(), valid_uid();
  extern int call_passmgmt(), edit_group(), create_home();
  extern int edit_project();
  extern int **valid_lgroup();
  extern projid_t **valid_lproject();
- extern void update_def(struct userdefs *);
- extern void import_def(struct userdefs *);
  extern int get_default_zfs_flags();
  
  static uid_t uid;                       /* new uid */
  static char *logname;                   /* login name to add */
  static struct userdefs *usrdefs;        /* defaults for useradd */
--- 93,102 ----