First release candidate for the 1.8.x series.

Latest bugfix release for 1.7.0.

Fifth bugfix release for 1.7.0.

Fourth bugfix release for 1.7.0.

Third bugfix release for 1.7.0.

Get a couple more LIBMESH_PETSC_NULLPTR

I was hoping to cherry-pick all of these fixes, but we've been taking
too long to get v1.8 out and there are a number of conflicts.

First bugfix release for 1.7.0.

Tag v1.7.0.

Tag third release candidate for the 1.7 series.

Tag second release candidate for the 1.7 series.