phonon.py: fix for current _required
phonon.py: fix for current _required

sfepy/sfepy,vlukes/sfepy,BubuLK/sfepy,rc/sfepy,sfepy/sfepy,rc/sfepy,BubuLK/sfepy,sfepy/sfepy,vlukes/sfepy,rc/sfepy,BubuLK/sfepy,vlukes/sfepy