Add support for USE_EXPAND

[Whissi]

When doing stabilization for packages using USE_EXPAND, app-admin/collectd or www-servers/nginx for example, tatt will currently ignore USE_EXPANDs as INVALID USE flags:

Bugnumber:  628540                                                                                                      Stabilization bug detected.
Jobname: collectd
Found the following package atom : =app-admin/collectd-5.7.2-r1
Unmasked =app-admin/collectd-5.7.2-r1 in /etc/portage/package.keywords/archtest
  =app-admin/collectd-5.7.2-r1: ignoring invalid USE flag combination ['collectd_plugins_aggregation', 'collectd_plugins
_apache', 'collectd_plugins_apcups', 'collectd_plugins_battery', 'collectd_plugins_bind', 'collectd_plugins_ceph', 'coll
ectd_plugins_conntrack', 'collectd_plugins_contextswitch', 'collectd_plugins_cpu', 'collectd_plugins_cpufreq', 'collectd
_plugins_csv', 'collectd_plugins_curl', 'collectd_plugins_curl_xml', 'collectd_plugins_dbi', 'collectd_plugins_df', 'col
lectd_plugins_disk', 'collectd_plugins_entropy', 'collectd_plugins_exec', 'collectd_plugins_fhcount', 'collectd_plugins_
gmond', 'collectd_plugins_hddtemp', 'collectd_plugins_interface', 'collectd_plugins_ipc', 'collectd_plugins_iptables', '
collectd_plugins_irq', 'collectd_plugins_logfile', 'collectd_plugins_madwifi', 'collectd_plugins_match_hashed', 'collect
d_plugins_match_timediff', 'collectd_plugins_match_value', 'collectd_plugins_memcachec', 'collectd_plugins_memory', 'col
lectd_plugins_modbus', 'collectd_plugins_multimeter', 'collectd_plugins_mysql', 'collectd_plugins_netlink', 'collectd_pl
ugins_notify_email', 'collectd_plugins_ntpd', 'collectd_plugins_numa', 'collectd_plugins_onewire', 'collectd_plugins_ope
nldap', 'collectd_plugins_openvpn', 'collectd_plugins_perl', 'collectd_plugins_processes', 'collectd_plugins_protocols', 'collectd_plugins_python', 'collectd_plugins_redis', 'collectd_plugins_rrdcached', 'collectd_plugins_rrdtool', 'collect
d_plugins_sensors', 'collectd_plugins_statsd', 'collectd_plugins_swap', 'collectd_plugins_table', 'collectd_plugins_target_replace', 'collectd_plugins_target_scale', 'collectd_plugins_target_set', 'collectd_plugins_ted', 'collectd_plugins_t
okyotyrant', 'collectd_plugins_unixsock', 'collectd_plugins_users', 'collectd_plugins_uuid', 'collectd_plugins_wireless', 'collectd_plugins_write_kafka', 'collectd_plugins_write_prometheus', 'collectd_plugins_write_redis', 'collectd_plugins_write_sensu', 'collectd_plugins_write_tsdb', 'collectd_plugins_xencpu', 'collectd_plugins_zfs_arc', 'collectd_plugins_zookeeper', 'contrib', 'static-libs', 'xfs']                 

[kensington]

I think this is a regression, it works fine in 0.5

[DerDakon]

I don't think it ignores that. The example above shows that it uses USE_EXPAND, it has just found one combination of that flags that is invalid. In fact, when I run tatt on that bug, it shows multiple combinations as invalid, but generates a use script that has several other of them.