fix default sub_precond value in PETScKrylovSolver
fix default sub_precond value in PETScKrylovSolver

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