fix the residuum of the iterated IMPES solver
put comment back in the right place
Merge pull request #230 from jdannberg/iterated_IMPES_fix

fix the residual of the iterated IMPES solver
Update comments in a couple of places.
Merge pull request #231 from bangerth/doc-update

Update comments in a couple of places.
add a test for the iterated IMPES solver
Merge pull request #232 from jdannberg/iterated_IMPES_test

add a test for the iterated IMPES solver
Handle change of output_interval during restart.
Merge pull request #236 from gassmoeller/visualization_fix

Always create a visualization output after restart if interval is set to 0
Added material model based on rheology in Morency and Doin, 2004
Merge pull request #158 from jperryhouts/morency_doin_material

Added material model based on rheology in Morency and Doin, 2004
Merged from geodynamics/master