Improve the wording of an exception.

I ran into this exception and couldn't figure out what's wrong without looking at the source code.
Update the documentation of VectorTools::project_boundary_values().

This had apparently confused a user on the mailing list earlier today, so structure the
documentation better.
Merge pull request #34 from bangerth/doc-fixes-2

Update the documentation of VectorTools::project_boundary_values() to make it clearer.
Improve the documentation of VectorTools::create_point_source_vector().

The previous version of the documentation was not exactly clear as to what the 'orientation' argument actually referred to.
Update documentation a bit.

Reading through the documentation of some of the functions in DoFTools, there are a number of functions for which I can't quite figure out what exactly they do. This updates a couple of places, but more work remains. In particular, I have no idea from the description of what DoFTools::make_single_patch() does.
Merge pull request #36 from bangerth/doc-fixes-4

Update documentation a bit.
Merge pull request #33 from bangerth/doc-fixes

Improve the wording of an exception.
Merge pull request #35 from bangerth/doc-fixes-3

Improve the documentation of VectorTools::create_point_source_vector().
Add more functions that deal with the infrastructure for solving local problems on patches around cells.

The functions DoFTools::count_dofs_on_patch() and DoFTools::map_global_dofs_to_patch_indices() help set up linear systems on patches. This is joint work with Arezou Ghesmati.
Merge pull request #37 from bangerth/add-patch-generators

Infrastructure functions for local problems on patches

The functions DoFTools::count_dofs_on_patch() and
DoFTools::map_global_dofs_to_patch_indices() help set up
linear systems on patches.
This is joint work with Arezou Ghesmati.