fix initial state argument handling in Problem.solve(), .block_solve()
fix initial state argument handling in Problem.solve(), .block_solve()

- new .set_default_state()

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