tolerance reduced for bicgstab-solver

demo/init/vecellipt.dat.3d

@@ -11,9 +11,9 @@ vecellipt->polynomial degree[1]:         1
 
 vecellipt->solver:                       bicgstab
 vecellipt->solver->max iteration:        1000
-vecellipt->solver->tolerance:            1.e-10
+vecellipt->solver->tolerance:            1.e-12
 vecellipt->solver->info:                 2
-vecellipt->solver->left precon:          diag
+vecellipt->solver->left precon:          ilu
 vecellipt->solver->right precon:         no
 
 vecellipt->estimator[0]:                 residual