simplify stiffness_from_lame() to consistently add two dimensions
simplify stiffness_from_lame() to consistently add two dimensions

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