Slightly improve warning

Old feature support macros which were tested until 2.4, kept around
for one more release. As these are now always supported due to the
new compiler requirements, they are directly defined without an
explicit test.

Document an incompatibility issue of index_sequence
and add a reminder to fix this as soon as we allow
template aliases.
This can only be fixed

GCC 4.4, I'm looking at you

We decided to have all stl like stuff in Dune::Std:: and not
in Std:: Besides our decision with the previous version tupleutility.hh
did not compile if a header refering to Dune::Std:: was included.

This uses perfect forwarding (following Herb Sutter) and
SFINAE (following Stephan T. Lavavej) to get a standard
comforming implementation also for array.

C++14 will introduce integer/index sequences in the header <utility>.
This patch introduces a backwards compatible implementation similar in
use. However, the implementation differs in the following technical
details:

  - index_sequence is not a template alias for integer_sequence but
  inherits from it

  - make_{integer, index}_sequence are not a template aliases but free
  standing functions

Both differences stem from the absence of template aliases introduced in
GCC aa late as gcc-4.7. This implementation will work in gcc-4.4 and
later.

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).