Apparently there used to be a time where the LeafIntersectionIterator
didn't work properly.  The finitevolume.cc example hacked around it,
and the how-to text contained a lengthy paragraph & illustration to explain
that hack.

Both hack and explanation are obsolete, and this patch removes them.

This fixes FS#1409.

[[Imported from SVN: r370]]

[[Imported from SVN: r337]]

[[Imported from SVN: r289]]

use the new center, centerUnitOuterNormal methods() of Dune::Geometry

[[Imported from SVN: r277]]

[[Imported from SVN: r267]]

 GridViews instead of the grid directly.

creadits to Martin Drohmann

[[Imported from SVN: r238]]

[[Imported from SVN: r215]]

[[Imported from SVN: r188]]

[[Imported from SVN: r174]]

   the correct line numbers in the howto
 * adjusted the global refinement und the dimension of the grid in
   visualization.cc
 * adjusted the number of refinement steps in integration.cc
 * several fixes in grid-howto.tex


[[Imported from SVN: r93]]

[[Imported from SVN: r89]]

[[Imported from SVN: r73]]

[[Imported from SVN: r59]]

[[Imported from SVN: r57]]

* fixed dune include paths

[[Imported from SVN: r56]]

[[Imported from SVN: r50]]

[[Imported from SVN: r38]]

checked shock speed in 2D and 3D for simplices.

[[Imported from SVN: r34]]

[[Imported from SVN: r27]]

[[Imported from SVN: r26]]

[[Imported from SVN: r14]]

still missing: Alberta intersection iterator conforming to interface

[[Imported from SVN: r13]]

still does not work portably on UG and Alberta

[[Imported from SVN: r12]]