Fix a bug that gives wrong velocity near the poles.
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Merge pull request #227 from SiqiZhang/gplate_fix

Fix a bug in gplate plugin: While gplate uses zero longitude at all grid points at poles, we assume the longitude at those points vary from 0 to 360. This results in a wrong velocity to be interpolated near the poles (the velocity between poles to the first latitude grid points would be wrong, however the velocity right at the pole will be OK).
Add test for gplates-3d.
Merge pull request #228 from gassmoeller/gplate_fix

Gplate fix
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.