Macro to use C++11 feature noexcept specifier.
Add test for CMake and autotools.

The classes AlwaysFalse, AlwaysTrue reside in the deprecated header
dune/common/static_assert, yet they are frequently used to document
template code (see FS#1435 for details). As the C++11 standard library
does not provide a straight forward replacement for theses classes, we
offer C++11 style reimplementations. The replacements to_false_type,
to_true_type reside in the namespace Std and are thus easily
identifiable as Dune specifis.

DUNE_FINAL is a helper macro for C++11 and should be placed in
std, where now all compatibility has to be placed.
Beautify Doxygen documentation.

This patch removes an extra header install command for tests. It
originally came when copying dune/common/CMakeLists.txt to
dune/common/std/CMakeLists.txt. Sorry for the noise.

The majority of developers favor individual headers for (emulation of) C++11
features over collecting them in a single header cxx11.hh. This patch
renames cxx11.hh to constexpr.hh and moves it into the subdirectory std.
This is the place most developers would like these headers in (see
http://users.dune-project.org/doodles/4).